diff --git a/ui/backend/app.py b/ui/backend/app.py
index 0777889..f6c01c9 100644
--- a/ui/backend/app.py
+++ b/ui/backend/app.py
@@ -145,6 +145,31 @@ def chat_pipeline(name: str):
         session_id = payload.get("session_id")
         dynamic_params = payload.get("dynamic_params", {})
 
+        selected_collection = dynamic_params.get("collection_name")
+
+        try:
+            kb_config = pm.load_kb_config()
+            milvus_global_config = kb_config.get("milvus", {})
+            
+            retriever_params = {
+                "index_backend": "milvus", 
+                "index_backend_configs": {
+                    "milvus": milvus_global_config 
+                }
+            }
+            
+            if selected_collection:
+                retriever_params["collection_name"] = selected_collection
+                print(f"debug: Chat using collection override: {selected_collection}")
+            
+            dynamic_params["retriever"] = retriever_params
+            
+            if "collection_name" in dynamic_params:
+                del dynamic_params["collection_name"]
+                
+        except Exception as e:
+            print(f"Warning: Failed to construct retriever config: {e}")
+
         if not session_id:
             return jsonify({"error": "session_id missing. Please start engine first."}), 400
         
diff --git a/ui/frontend/index.html b/ui/frontend/index.html
index dc469cc..da24db1 100644
--- a/ui/frontend/index.html
+++ b/ui/frontend/index.html
@@ -174,6 +174,16 @@ <h2 class="m-0 fs-5 fw-semibold">Parameter Configuration</h2>
       <div class="chat-container">
         <div class="chat-scroll-area" id="chat-history"></div>
         <div class="chat-input-wrapper">
+          <div class="d-flex justify-content-between align-items-center mb-2 px-1">
+             <div class="d-flex align-items-center gap-2">
+                <select id="chat-collection-select" class="form-select form-select-sm" style="width: auto; border-radius: 20px; font-size: 0.8rem; background-color: #f8f9fa;">
+                   <option value="" selected>⚪ No Knowledge Base</option>
+                   </select>
+                <button class="btn btn-sm btn-icon text-muted" onclick="renderChatCollectionOptions()" title="Refresh Collections">↻</button>
+             </div>
+             <span class="text-xs text-muted" id="chat-kb-status"></span>
+          </div>
+
           <form id="chat-form" class="chat-input-container shadow-sm">
             <input type="text" id="chat-input" class="form-control chat-input" placeholder="Message UltraRAG..." autocomplete="off" />
             
diff --git a/ui/frontend/main.js b/ui/frontend/main.js
index d0318eb..3c5b2df 100644
--- a/ui/frontend/main.js
+++ b/ui/frontend/main.js
@@ -77,6 +77,7 @@ const els = {
   chatNewBtn: document.getElementById("chat-new-btn"),
   chatSessionList: document.getElementById("chat-session-list"),
   demoToggleBtn: document.getElementById("demo-toggle-btn"), // 引擎开关
+  chatCollectionSelect: document.getElementById("chat-collection-select"),
 
   // [新增] 视图容器
   chatMainView: document.getElementById("chat-main-view"),
@@ -800,6 +801,41 @@ function updateDemoControls() {
 
 // --- Chat Logic (Updated with Streaming) ---
 
+// [新增] 渲染聊天界面的 Collection 下拉选项
+async function renderChatCollectionOptions() {
+    if (!els.chatCollectionSelect) return;
+    
+    // 保存当前选中的值，以免刷新后重置
+    const currentVal = els.chatCollectionSelect.value;
+    
+    try {
+        // 复用后端的列表接口
+        const data = await fetchJSON('/api/kb/files');
+        const collections = data.index || []; // data.index 存放的是 collection 列表
+        
+        els.chatCollectionSelect.innerHTML = '<option value="">⚪ No Knowledge Base</option>';
+        
+        collections.forEach(c => {
+            const opt = document.createElement("option");
+            opt.value = c.name;
+            // 显示名字和数据量
+            opt.textContent = `${c.name} (${c.count || 0})`;
+            els.chatCollectionSelect.appendChild(opt);
+        });
+        
+        // 尝试恢复选中状态
+        if (currentVal) {
+            // 检查新列表里是否还有这个值
+            const exists = collections.find(c => c.name === currentVal);
+            if (exists) els.chatCollectionSelect.value = currentVal;
+        }
+        
+    } catch (e) {
+        console.error("Failed to load collections for chat:", e);
+        // 出错时不覆盖默认选项，或者显示错误
+    }
+}
+
 // [新增] 切换到知识库视图
 function openKBView() {
     if (!els.chatMainView || !els.kbMainView) return;
@@ -1211,6 +1247,9 @@ function openChatView() {
   if (els.chatPipelineName) els.chatPipelineName.textContent = state.selectedPipeline || "—";
 
   renderChatPipelineMenu();
+
+  // [新增] 进入聊天时，加载最新的 Collection 列表
+  renderChatCollectionOptions();
   
   if (!state.chat.currentSessionId) createNewChatSession();
   
@@ -1456,10 +1495,21 @@ async function handleChatSubmit(event) {
 
   try {
     if (!state.parametersReady) await persistParameterData({ silent: true });
+
+    const selectedCollection = els.chatCollectionSelect ? els.chatCollectionSelect.value : "";
+    
+    const dynamicParams = {};
+    if (selectedCollection) {
+        dynamicParams["collection_name"] = selectedCollection;
+    }
+
     const endpoint = `/api/pipelines/${encodeURIComponent(state.selectedPipeline)}/chat`;
     const body = JSON.stringify({ 
-        question, history: state.chat.history, is_demo: true, 
-        session_id: state.chat.engineSessionId, dynamic_params: {} 
+        question, 
+        history: state.chat.history, 
+        is_demo: true, 
+        session_id: state.chat.engineSessionId, 
+        dynamic_params: dynamicParams
     });
     
     const response = await fetch(endpoint, {
diff --git a/ui/frontend/style.css b/ui/frontend/style.css
index 68ae3c6..a322f9e 100644
--- a/ui/frontend/style.css
+++ b/ui/frontend/style.css
@@ -1199,4 +1199,26 @@ body {
     display: flex;
     justify-content: space-between;
 }
-.folder-file-row:last-child { border-bottom: none; }
\ No newline at end of file
+.folder-file-row:last-child { border-bottom: none; }
+
+/* Chat Context Selector */
+#chat-collection-select {
+  border-color: var(--border-subtle);
+  cursor: pointer;
+  padding-left: 12px;
+  padding-right: 32px; /* 留出箭头空间 */
+  font-weight: 500;
+  color: var(--text-primary);
+  box-shadow: none;
+  transition: all 0.2s;
+}
+
+#chat-collection-select:hover {
+  background-color: #fff;
+  border-color: var(--accent-blue);
+}
+
+#chat-collection-select:focus {
+  border-color: var(--accent-blue);
+  box-shadow: 0 0 0 2px rgba(37, 99, 235, 0.1);
+}
\ No newline at end of file