diff --git a/apps/web/src/components/editor/PreviewPanel.vue b/apps/web/src/components/editor/PreviewPanel.vue
index a1d346e5c..0b501bb04 100644
--- a/apps/web/src/components/editor/PreviewPanel.vue
+++ b/apps/web/src/components/editor/PreviewPanel.vue
@@ -1,9 +1,11 @@
 <script setup lang="ts">
+import type { DiagramDownloadOverlay } from '@/utils/diagramDownload'
 import { highlightPendingBlocks, hljs } from '@md/core'
 import { useRenderStore } from '@/stores/render'
 import { useUIStore } from '@/stores/ui'
+import { setupDiagramDownloadOverlay } from '@/utils/diagramDownload'
 
-defineProps<{
+const props = defineProps<{
   backLight: boolean
   isCoping: boolean
   onContentClick: (event: MouseEvent) => void
@@ -32,6 +34,33 @@ watch(output, () => {
   })
 })
 
+let diagramOverlay: DiagramDownloadOverlay | null = null
+
+// Pause bar injection for the entire duration of isCoping so that
+// processClipboardContent mutations never re-inject bars, and resume
+// after the copy pipeline resets the DOM.
+watch(() => props.isCoping, (coping) => {
+  if (coping) {
+    diagramOverlay?.pause()
+  }
+  else {
+    nextTick(() => diagramOverlay?.resume())
+  }
+})
+
+onMounted(() => {
+  nextTick(() => {
+    const outputEl = document.getElementById(`output`)
+    if (outputEl) {
+      diagramOverlay = setupDiagramDownloadOverlay(outputEl)
+    }
+  })
+})
+
+onUnmounted(() => {
+  diagramOverlay?.cleanup()
+})
+
 defineExpose({
   previewRef,
 })
@@ -124,3 +153,95 @@ defineExpose({
   border-spacing: 0;
 }
 </style>
+
+<style>
+/* Diagram download overlay — unscoped to affect v-html content */
+.mermaid-diagram,
+.plantuml-diagram {
+  position: relative;
+}
+
+.diagram-download-bar {
+  position: absolute;
+  top: 8px;
+  right: 8px;
+  z-index: 10;
+  display: flex;
+  gap: 4px;
+  opacity: 0;
+  visibility: hidden;
+  pointer-events: none;
+  transform: translateY(-6px);
+  transition: opacity 0.18s ease, transform 0.18s ease, visibility 0s 0.18s;
+}
+
+.mermaid-diagram:hover .diagram-download-bar,
+.plantuml-diagram:hover .diagram-download-bar,
+.mermaid-diagram:focus-within .diagram-download-bar,
+.plantuml-diagram:focus-within .diagram-download-bar {
+  opacity: 1;
+  visibility: visible;
+  pointer-events: auto;
+  transform: translateY(0);
+  transition: opacity 0.18s ease, transform 0.18s ease, visibility 0s;
+}
+
+.diagram-download-btn {
+  display: inline-flex;
+  align-items: center;
+  gap: 3px;
+  padding: 4px 9px;
+  font-size: 11px;
+  font-weight: 600;
+  letter-spacing: 0.05em;
+  text-transform: uppercase;
+  border-radius: 6px;
+  border: 1px solid rgba(0, 0, 0, 0.1);
+  background: rgba(255, 255, 255, 0.88);
+  color: #444;
+  backdrop-filter: blur(10px);
+  -webkit-backdrop-filter: blur(10px);
+  cursor: pointer;
+  box-shadow: 0 1px 4px rgba(0, 0, 0, 0.1), 0 0 0 0.5px rgba(0, 0, 0, 0.06);
+  transition: background 0.15s ease, box-shadow 0.15s ease, color 0.15s ease, transform 0.1s ease;
+  user-select: none;
+  font-family: system-ui, -apple-system, sans-serif;
+  line-height: 1;
+  white-space: nowrap;
+}
+
+.diagram-download-btn:hover {
+  background: rgba(255, 255, 255, 0.98);
+  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.14), 0 0 0 0.5px rgba(0, 0, 0, 0.08);
+  color: #111;
+}
+
+.diagram-download-btn:active {
+  transform: scale(0.95);
+}
+
+.diagram-download-btn:disabled {
+  opacity: 0.5;
+  pointer-events: none;
+}
+
+.diagram-btn-loading {
+  letter-spacing: 0.1em;
+  opacity: 0.7;
+}
+
+/* Dark mode */
+.output_night .diagram-download-btn {
+  background: rgba(30, 32, 38, 0.88);
+  border-color: rgba(255, 255, 255, 0.1);
+  color: #b8bcc8;
+  box-shadow: 0 1px 4px rgba(0, 0, 0, 0.4), 0 0 0 0.5px rgba(255, 255, 255, 0.04);
+}
+
+.output_night .diagram-download-btn:hover {
+  background: rgba(50, 53, 62, 0.96);
+  border-color: rgba(255, 255, 255, 0.18);
+  color: #fff;
+  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.5);
+}
+</style>
diff --git a/apps/web/src/stores/export.ts b/apps/web/src/stores/export.ts
index 807ea1545..db38cbb16 100644
--- a/apps/web/src/stores/export.ts
+++ b/apps/web/src/stores/export.ts
@@ -57,9 +57,10 @@ export const useExportStore = defineStore(`export`, () => {
     if (!el)
       return
 
-    // 添加临时样式：禁用代码块滚动，启用换行
+    // 添加临时样式：禁用代码块滚动，启用换行，隐藏仅用于预览的 UI 覆盖层
     const style = document.createElement('style')
     style.textContent = `
+      .diagram-download-bar { display: none !important; }
       .preview pre.code__pre,
       .preview .hljs.code__pre,
       .preview pre.code__pre > code,
diff --git a/apps/web/src/utils/diagramDownload.ts b/apps/web/src/utils/diagramDownload.ts
new file mode 100644
index 000000000..9b9e327b1
--- /dev/null
+++ b/apps/web/src/utils/diagramDownload.ts
@@ -0,0 +1,203 @@
+/**
+ * Diagram download utilities
+ * Supports downloading SVG diagrams (Mermaid, PlantUML, etc.) as .svg or .png
+ */
+
+const DOWNLOAD_ICON = `<svg xmlns="http://www.w3.org/2000/svg" width="11" height="11" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2.5" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="M21 15v4a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2v-4"/><polyline points="7 10 12 15 17 10"/><line x1="12" y1="15" x2="12" y2="3"/></svg>`
+
+const DIAGRAM_SELECTORS = `.mermaid-diagram, .plantuml-diagram`
+
+// ─── Download helpers ────────────────────────────────────────────────────────
+
+function triggerDownload(url: string, filename: string): void {
+  const a = document.createElement(`a`)
+  a.href = url
+  a.download = filename
+  a.style.display = `none`
+  document.body.appendChild(a)
+  a.click()
+  document.body.removeChild(a)
+}
+
+function cloneSvg(svgEl: SVGSVGElement): SVGSVGElement {
+  const clone = svgEl.cloneNode(true) as SVGSVGElement
+  if (!clone.hasAttribute(`xmlns`))
+    clone.setAttribute(`xmlns`, `http://www.w3.org/2000/svg`)
+  return clone
+}
+
+export function downloadDiagramSvg(svgEl: SVGSVGElement, filename = `diagram`): void {
+  const svgStr = new XMLSerializer().serializeToString(cloneSvg(svgEl))
+  const blob = new Blob([svgStr], { type: `image/svg+xml;charset=utf-8` })
+  const url = URL.createObjectURL(blob)
+  triggerDownload(url, `${filename}.svg`)
+  URL.revokeObjectURL(url)
+}
+
+export function downloadDiagramPng(svgEl: SVGSVGElement, filename = `diagram`): Promise<void> {
+  const rect = svgEl.getBoundingClientRect()
+  const width = rect.width || svgEl.viewBox?.baseVal?.width || 800
+  const height = rect.height || svgEl.viewBox?.baseVal?.height || 600
+  const scale = Math.max(2, window.devicePixelRatio)
+
+  const clone = cloneSvg(svgEl)
+  clone.setAttribute(`width`, String(width))
+  clone.setAttribute(`height`, String(height))
+
+  const svgStr = new XMLSerializer().serializeToString(clone)
+  // Use a percent-encoded data URL instead of a blob URL: drawing a blob-URL
+  // image onto canvas triggers a SecurityError ("tainted canvas") in Chromium.
+  // Data URLs are treated as same-origin and avoid this restriction.
+  const dataUrl = `data:image/svg+xml;charset=utf-8,${encodeURIComponent(svgStr)}`
+
+  return new Promise((resolve, reject) => {
+    const img = new Image()
+    img.onload = () => {
+      const canvas = document.createElement(`canvas`)
+      canvas.width = Math.round(width * scale)
+      canvas.height = Math.round(height * scale)
+      const ctx = canvas.getContext(`2d`)
+      if (!ctx) {
+        reject(new Error(`No 2D canvas context`))
+        return
+      }
+      ctx.fillStyle = `#ffffff`
+      ctx.fillRect(0, 0, canvas.width, canvas.height)
+      ctx.scale(scale, scale)
+      ctx.drawImage(img, 0, 0, width, height)
+      canvas.toBlob((blob) => {
+        if (!blob) {
+          reject(new Error(`PNG blob generation failed`))
+          return
+        }
+        const url = URL.createObjectURL(blob)
+        triggerDownload(url, `${filename}.png`)
+        URL.revokeObjectURL(url)
+        resolve()
+      }, `image/png`)
+    }
+    img.onerror = () => reject(new Error(`Failed to load SVG as image`))
+    img.src = dataUrl
+  })
+}
+
+// ─── Download bar DOM injection ───────────────────────────────────────────────
+
+function makeButton(label: string, title: string): HTMLButtonElement {
+  const btn = document.createElement(`button`)
+  btn.className = `diagram-download-btn`
+  btn.type = `button`
+  btn.title = title
+  btn.innerHTML = `${DOWNLOAD_ICON}<span>${label}</span>`
+  return btn
+}
+
+function createDownloadBar(container: HTMLElement, idx: number): HTMLDivElement {
+  const bar = document.createElement(`div`)
+  bar.className = `diagram-download-bar`
+
+  const svgBtn = makeButton(`SVG`, `下载为 SVG`)
+  svgBtn.addEventListener(`click`, (e) => {
+    e.preventDefault()
+    e.stopPropagation()
+    const svg = container.querySelector<SVGSVGElement>(`svg`)
+    if (svg)
+      downloadDiagramSvg(svg, `diagram-${idx}`)
+  })
+
+  const pngBtn = makeButton(`PNG`, `下载为 PNG`)
+  pngBtn.addEventListener(`click`, async (e) => {
+    e.preventDefault()
+    e.stopPropagation()
+    const svg = container.querySelector<SVGSVGElement>(`svg`)
+    if (!svg)
+      return
+    pngBtn.disabled = true
+    const saved = pngBtn.innerHTML
+    pngBtn.innerHTML = `<span class="diagram-btn-loading">•••</span>`
+    try {
+      await downloadDiagramPng(svg, `diagram-${idx}`)
+    }
+    finally {
+      pngBtn.disabled = false
+      pngBtn.innerHTML = saved
+    }
+  })
+
+  bar.append(svgBtn, pngBtn)
+  return bar
+}
+
+function injectBar(container: HTMLElement, idx: number): void {
+  if (getComputedStyle(container).position === `static`)
+    container.style.position = `relative`
+  container.querySelector(`.diagram-download-bar`)?.remove()
+  container.appendChild(createDownloadBar(container, idx))
+}
+
+// ─── Overlay lifecycle ────────────────────────────────────────────────────────
+
+export interface DiagramDownloadOverlay {
+  /** Permanently disconnect the observer — call on component unmount. */
+  cleanup: () => void
+  /** Remove all bars and stop injection. Call before copying / exporting. */
+  pause: () => void
+  /** Re-inject bars and resume injection. Call after copying / exporting. */
+  resume: () => void
+}
+
+/**
+ * Watches `outputEl` for diagram containers gaining SVG content and injects
+ * a SVG / PNG download bar into each one.
+ */
+export function setupDiagramDownloadOverlay(outputEl: HTMLElement): DiagramDownloadOverlay {
+  let paused = false
+  let counter = 0
+
+  function inject(el: HTMLElement) {
+    if (!paused && el.querySelector(`svg`) && !el.querySelector(`.diagram-download-bar`))
+      injectBar(el, ++counter)
+  }
+
+  function scan() {
+    outputEl.querySelectorAll<HTMLElement>(DIAGRAM_SELECTORS).forEach(inject)
+  }
+
+  scan()
+
+  let rafId: ReturnType<typeof requestAnimationFrame> | null = null
+
+  const observer = new MutationObserver(() => {
+    if (paused)
+      return
+    if (rafId !== null)
+      return
+    rafId = requestAnimationFrame(() => {
+      rafId = null
+      if (!paused)
+        scan()
+    })
+  })
+
+  observer.observe(outputEl, { childList: true, subtree: true })
+
+  return {
+    cleanup: () => {
+      if (rafId !== null)
+        cancelAnimationFrame(rafId)
+      observer.disconnect()
+    },
+    pause: () => {
+      paused = true
+      if (rafId !== null) {
+        cancelAnimationFrame(rafId)
+        rafId = null
+      }
+      outputEl.querySelectorAll(`.diagram-download-bar`).forEach(el => el.remove())
+    },
+    resume: () => {
+      paused = false
+      scan()
+    },
+  }
+}
diff --git a/apps/web/src/utils/index.ts b/apps/web/src/utils/index.ts
index f8a171242..bcc032c70 100644
--- a/apps/web/src/utils/index.ts
+++ b/apps/web/src/utils/index.ts
@@ -81,7 +81,11 @@ export async function exportPostsAsZip(posts: Array<{ title: string, content: st
  */
 export function getHtmlContent(): string {
   const element = document.querySelector(`#output`)!
-  return element.innerHTML
+  // Clone to avoid mutating the live DOM, then strip injected UI overlays
+  // (e.g. diagram download bars) that must not appear in exported content.
+  const clone = element.cloneNode(true) as HTMLElement
+  clone.querySelectorAll(`.diagram-download-bar`).forEach(el => el.remove())
+  return clone.innerHTML
 }
 
 /**