diff --git a/.env.example b/.env.example
index a6a2881..df710a1 100644
--- a/.env.example
+++ b/.env.example
@@ -8,6 +8,7 @@ WISEGRADE_SECRET_KEY=replace-with-a-random-32-character-secret
 EMBEDDING_MODEL_NAME=BAAI/bge-m3
 EMBEDDING_MODEL_PATH=/models/bge-m3
 EMBEDDING_MODEL_VERSION=local
+OCR_MODEL_DIR=/models/ocr
 MODEL_TIMEOUT_SECONDS=120
 MODEL_CONCURRENCY=2
 MODEL_RETRIES=2
diff --git a/backend/tests/test_parsing.py b/backend/tests/test_parsing.py
index 8dd2195..07136a1 100644
--- a/backend/tests/test_parsing.py
+++ b/backend/tests/test_parsing.py
@@ -6,7 +6,7 @@ from docx import Document
 from pptx import Presentation
 from pptx.util import Inches
 
-from wisegrade.parsing import parse_document
+from wisegrade.parsing import _ocr_engine, parse_document
 
 
 def test_pdf_pages_and_images(tmp_path):
@@ -20,6 +20,11 @@ def test_pdf_pages_and_images(tmp_path):
     assert (tmp_path / "assets" / "page-1.png").exists()
 
 
+def test_scanned_pdf_requires_offline_ocr_package(tmp_path):
+    with pytest.raises(RuntimeError, match="离线OCR模型目录"):
+        _ocr_engine(str(tmp_path / "missing-ocr"))
+
+
 @pytest.mark.skipif(not shutil.which("libreoffice"), reason="LibreOffice is installed in the deployment image")
 def test_docx_and_pptx_render(tmp_path):
     word = Document()
diff --git a/backend/wisegrade/config.py b/backend/wisegrade/config.py
index 890a582..4d46579 100644
--- a/backend/wisegrade/config.py
+++ b/backend/wisegrade/config.py
@@ -19,6 +19,7 @@ class Settings(BaseSettings):
     embedding_model_name: str = "BAAI/bge-m3"
     embedding_model_path: Path = Path("/models/bge-m3")
     embedding_model_version: str = "local"
+    ocr_model_dir: Path = Path("/models/ocr")
     model_timeout_seconds: int = 120
     model_concurrency: int = 2
     model_retries: int = 2
diff --git a/backend/wisegrade/parsing.py b/backend/wisegrade/parsing.py
index 6b6dfb1..dc7fb2b 100644
--- a/backend/wisegrade/parsing.py
+++ b/backend/wisegrade/parsing.py
@@ -1,11 +1,18 @@
 import subprocess
 import tempfile
+from functools import lru_cache
 from pathlib import Path
+from threading import Lock
 
 import pymupdf as fitz
 from docx import Document
 from pptx import Presentation
 
+from .config import get_settings
+
+
+_ocr_lock = Lock()
+
 
 def _render(page, output: Path):
     output.parent.mkdir(parents=True, exist_ok=True)
@@ -13,15 +20,30 @@ def _render(page, output: Path):
     return str(output)
 
 
-def _ocr(image_path: str):
+@lru_cache(maxsize=1)
+def _ocr_engine(model_dir: str):
+    root = Path(model_dir)
+    detection, recognition = root / "detection", root / "recognition"
+    if not detection.is_dir() or not recognition.is_dir():
+        raise RuntimeError(f"扫描PDF需要离线OCR模型目录: {detection} 和 {recognition}")
     try:
         from paddleocr import PaddleOCR
     except ImportError as exc:
         raise RuntimeError("扫描PDF需要PaddleOCR；请安装OCR依赖或交由教师处理") from exc
     try:
-        engine = PaddleOCR(lang="ch", use_textline_orientation=True)
+        return PaddleOCR(lang="ch", text_detection_model_dir=str(detection), text_recognition_model_dir=str(recognition),
+                         use_textline_orientation=False, use_doc_orientation_classify=False, use_doc_unwarping=False)
     except TypeError:
-        engine = PaddleOCR(use_angle_cls=True, lang="ch", show_log=False)
+        return PaddleOCR(lang="ch", det_model_dir=str(detection), rec_model_dir=str(recognition), use_angle_cls=False, show_log=False)
+
+
+def _ocr(image_path: str):
+    engine = _ocr_engine(str(get_settings().ocr_model_dir))
+    with _ocr_lock:
+        return _ocr_unlocked(engine, image_path)
+
+
+def _ocr_unlocked(engine, image_path: str):
     if hasattr(engine, "predict"):
         result = engine.predict(image_path)
         lines = []
diff --git a/docs/DEPLOYMENT.md b/docs/DEPLOYMENT.md
index ace0a85..a3177ec 100644
--- a/docs/DEPLOYMENT.md
+++ b/docs/DEPLOYMENT.md
@@ -59,7 +59,7 @@ EMBEDDING_MODEL_VERSION=your-package-version
 
 `EMBEDDING_MODEL_VERSION` 会写入每个评分批次快照。若模型目录缺失或内容不完整，导入仍可完成，知识库入库和评分会显示错误。可离线分发 `docker save` 生成的镜像包及单独的 `models-bge-m3.tar.zst`；目标机执行 `docker load -i docker-images.tar` 后解压模型包，运行相同的 Compose 配置。
 
-扫描 PDF 的 OCR 使用 PaddleOCR；需在离线环境准备其运行所需的 OCR 模型缓存。没有 OCR 模型且 PDF 无可提取文字时，文件进入解析失败状态并显示原因。
+扫描 PDF 的 OCR 使用 PaddleOCR。离线 OCR 包放在 `models/ocr/detection/` 和 `models/ocr/recognition/`，或修改 `OCR_MODEL_DIR` 指向包含这两个子目录的位置。没有 OCR 模型且 PDF 无可提取文字时，文件进入解析失败状态并显示原因；系统不会在解析时自动下载 OCR 模型。
 
 ## 教师操作