diff --git a/src/zotero_kb/templates/index.html b/src/zotero_kb/templates/index.html
index 708d0cf..0231bf9 100644
--- a/src/zotero_kb/templates/index.html
+++ b/src/zotero_kb/templates/index.html
@@ -418,6 +418,10 @@
             : []
         ),
         visibleCollectionItems: [],
+        collectionItemsLoaded: false,
+        loadingCollectionKey: null,
+        nextCollectionItemsRequestToken: 0,
+        activeCollectionItemsRequestToken: 0,
       };
 
       const elements = {
@@ -599,7 +603,7 @@
         syncCurrentProjectLabels();
         elements.importSelectedItemsButton.disabled = !hasProject || !hasSelection;
         elements.importSelectedItemsButton.title = !hasProject ? "请先选择项目" : (hasSelection ? "" : "请先选择文献");
-        elements.selectDescendantsButton.disabled = !state.visibleCollectionItems.length;
+        elements.selectDescendantsButton.disabled = !state.collectionItemsLoaded || !state.visibleCollectionItems.length;
         elements.clearSelectionButton.disabled = !state.selectedItemKeys.size;
         renderSelectedCount();
       }
@@ -719,6 +723,11 @@
           updateImportActionState();
           return;
         }
+        if (!state.collectionItemsLoaded) {
+          elements.collectionItems.innerHTML = '<div class="empty">正在加载当前 collection 文献。</div>';
+          updateImportActionState();
+          return;
+        }
         if (!state.visibleCollectionItems.length) {
           elements.collectionItems.innerHTML = '<div class="empty">当前目录及子目录下没有可导入文献。</div>';
           updateImportActionState();
@@ -759,14 +768,21 @@
           return;
         }
         state.visibleCollectionItems = [];
+        state.collectionItemsLoaded = false;
+        state.loadingCollectionKey = null;
         renderCollectionItems();
         setStatus(elements.collectionStatus, "");
       }
 
       async function loadCollectionItems(collectionKey) {
+        if (!state.collectionItemsLoaded && state.loadingCollectionKey === collectionKey) {
+          return;
+        }
         state.selectedCollectionKey = collectionKey;
         if (normalizeSelectedCollectionKey() !== collectionKey) {
           state.visibleCollectionItems = [];
+          state.collectionItemsLoaded = false;
+          state.loadingCollectionKey = null;
           renderCollectionTree();
           renderCollectionItems();
           setStatus(elements.collectionStatus, state.selectedCollectionKey ? "已切换到可用 collection。" : "");
@@ -778,9 +794,20 @@
         ensureSelectedCollectionExpanded();
         persistImportSessionState();
         renderCollectionTree();
+        state.collectionItemsLoaded = false;
+        state.loadingCollectionKey = collectionKey;
+        const requestToken = state.nextCollectionItemsRequestToken + 1;
+        state.nextCollectionItemsRequestToken = requestToken;
+        state.activeCollectionItemsRequestToken = requestToken;
+        renderCollectionItems();
         setStatus(elements.collectionStatus, "正在加载文献...");
         const payload = await api(`/api/zotero/collections/${collectionKey}/items`);
+        if (state.activeCollectionItemsRequestToken !== requestToken || state.selectedCollectionKey !== collectionKey) {
+          return;
+        }
         state.visibleCollectionItems = Array.isArray(payload.items) ? payload.items : [];
+        state.collectionItemsLoaded = true;
+        state.loadingCollectionKey = null;
         renderCollectionItems();
         const visibleCount = state.visibleCollectionItems.length;
         setStatus(
@@ -847,7 +874,10 @@
           } catch (error) {
             setStatus(elements.collectionStatus, error.message, true);
           }
-        } else if (state.selectedCollectionKey && !state.visibleCollectionItems.length) {
+        } else if (
+          state.selectedCollectionKey &&
+          (!state.collectionItemsLoaded && state.loadingCollectionKey !== state.selectedCollectionKey)
+        ) {
           try {
             await loadCollectionItems(state.selectedCollectionKey);
           } catch (error) {
diff --git a/tests/test_ui.py b/tests/test_ui.py
index eae301e..f595b7a 100644
--- a/tests/test_ui.py
+++ b/tests/test_ui.py
@@ -42,6 +42,8 @@ def test_index_contains_import_modal_controls(tmp_path) -> None:
     assert 'const ABSTRACT_PREVIEW_DELAY_MS = 3000;' in html
     assert 'isImportModalOpen: false' in html
     assert "currentProjectName: null" in html
+    assert "collectionItemsLoaded: false" in html
+    assert "nextCollectionItemsRequestToken: 0" in html
     assert "function openImportModal()" in html
     assert "function closeImportModal()" in html
     assert "function updateImportActionState()" in html