diff --git a/static/js/diff-viewer.js b/static/js/diff-viewer.js
index 79016bd..b75e107 100644
--- a/static/js/diff-viewer.js
+++ b/static/js/diff-viewer.js
@@ -199,6 +199,34 @@ const DiffViewer = {
         }
     },
 
+    // ── Diff too large guard ────────────────────────────────────────
+
+    _isTooLarge(files) {
+        const MAX_FILES = 300;
+        const MAX_LINES = 10000;
+        const totalAdd = files.reduce((s, f) => s + (f.additions || 0), 0);
+        const totalDel = files.reduce((s, f) => s + (f.deletions || 0), 0);
+        return files.length > MAX_FILES || (totalAdd + totalDel) > MAX_LINES;
+    },
+
+    _renderTooLargeWarning(files, totalAdd, totalDel, onExpand) {
+        const id = 'diff-expand-' + Math.random().toString(36).slice(2, 8);
+        this.container.innerHTML = `
+            <div class="bg-yellow-50 border border-yellow-200 rounded-lg p-6 text-center">
+                <div class="text-yellow-600 text-lg font-medium mb-2">⚠️ 变更过大，已跳过渲染</div>
+                <p class="text-sm text-gray-600 mb-1">
+                    共 <strong>${files.length}</strong> 个文件，
+                    <span class="text-green-600">+${totalAdd}</span>
+                    <span class="text-red-600">-${totalDel}</span>
+                </p>
+                <p class="text-xs text-gray-400 mb-4">渲染大量变更可能导致浏览器卡顿</p>
+                <button id="${id}" class="px-4 py-2 bg-blue-600 text-white text-sm rounded-md hover:bg-blue-700">
+                    显示 Diff
+                </button>
+            </div>`;
+        document.getElementById(id).addEventListener('click', onExpand);
+    },
+
     // ── Incremental rendering pipeline ──────────────────────────────
 
     // Render diff with file tree sidebar — incremental, non-blocking
@@ -213,6 +241,17 @@ const DiffViewer = {
 
         // Parse files for tree (fast — just regex + string ops)
         this.files = this._parseDiffFiles(diffString);
+
+        // Guard: if diff is too large, show warning instead of rendering
+        if (!options.forceRender && this._isTooLarge(this.files)) {
+            const totalAdd = this.files.reduce((s, f) => s + f.additions, 0);
+            const totalDel = this.files.reduce((s, f) => s + f.deletions, 0);
+            const self = this;
+            this._renderTooLargeWarning(this.files, totalAdd, totalDel, function () {
+                self.renderDiff(diffString, { ...options, forceRender: true });
+            });
+            return;
+        }
         const tree = this._buildTree(this.files);
 
         // Split diff into per-file chunks for incremental rendering
@@ -285,6 +324,17 @@ const DiffViewer = {
         const combinedDiff = files.map(f => f.patch).join('\n');
         this.rawDiff = combinedDiff;
 
+        // Guard: if diff is too large, show warning
+        if (!options.forceRender && this._isTooLarge(this.files)) {
+            const totalAdd = this.files.reduce((s, f) => s + f.additions, 0);
+            const totalDel = this.files.reduce((s, f) => s + f.deletions, 0);
+            const self = this;
+            this._renderTooLargeWarning(this.files, totalAdd, totalDel, function () {
+                self.renderFiles(files, { ...options, forceRender: true });
+            });
+            return;
+        }
+
         // Split into per-file chunks
         this._chunks = this.files.map(f => f._patch).filter(Boolean);
         this._chunkIndex = 0;