diff --git a/backend/database.py b/backend/database.py
index 0409ec0..2e69c60 100644
--- a/backend/database.py
+++ b/backend/database.py
@@ -4,8 +4,8 @@ from sqlalchemy.orm import sessionmaker
 import os
 from dotenv import load_dotenv
 
-# Load environment variables
-load_dotenv()
+# Load environment variables（override=True：.env 覆盖已有环境变量，避免系统里 DEBUG=true 导致与 .env 中 DEBUG=False 冲突）
+load_dotenv(override=True)
 
 # Database configuration
 DATABASE_HOST = os.getenv("DATABASE_HOST", "localhost")
diff --git a/backend/main.py b/backend/main.py
index 717eeb5..df9620c 100644
--- a/backend/main.py
+++ b/backend/main.py
@@ -10,7 +10,7 @@ from routes.auth import router as auth_router
 from security import get_current_user
 
 # Load environment variables
-load_dotenv()
+load_dotenv(override=True)
 
 # Configure logging
 logging.basicConfig(
diff --git a/backend/ota_storage.py b/backend/ota_storage.py
index face3a6..248e08b 100644
--- a/backend/ota_storage.py
+++ b/backend/ota_storage.py
@@ -16,13 +16,9 @@ OTA_MODEL_X8 = "Luxsin-X8"
 OTA_MODEL_X9 = "Luxsin-X9"
 OTA_UPLOAD_MODELS = {OTA_MODEL_X8, OTA_MODEL_X9}
 
-# 本地根目录；实际文件路径为 {根}/{md5前5位}/LUXSIN.PKG
-OTA_UPLOAD_DIR_DEV = os.getenv(
-    "OTA_UPLOAD_DIR_DEV", "H:/soft/projects/luxsin/dashboard/ota"
-)
-OTA_UPLOAD_DIR_PROD = os.getenv(
-    "OTA_UPLOAD_DIR_PROD", "/data/project/dashboard/upload"
-)
+# 默认本地根目录；实际路径为 {根}/{md5前5位}/LUXSIN.PKG（具体目录在 get_ota_upload_dir 内按当前环境读取）
+_OTA_UPLOAD_DIR_DEV_DEFAULT = "H:/soft/projects/luxsin/dashboard/ota"
+_OTA_UPLOAD_DIR_PROD_DEFAULT = "/data/project/dashboard/upload"
 
 AWS_REGION = os.getenv("AWS_REGION", "eu-central-1")
 AWS_ACCESS_KEY_ID = os.getenv("AWS_ACCESS_KEY_ID", "")
@@ -39,8 +35,12 @@ OTA_FILENAME_X9 = "LUXSIN.PKG"
 
 
 def get_ota_upload_dir() -> Path:
-    is_dev = os.getenv("DEBUG", "False").lower() in ("true", "1", "yes")
-    raw = OTA_UPLOAD_DIR_DEV if is_dev else OTA_UPLOAD_DIR_PROD
+    """按 DEBUG 选开发/生产目录；每次调用重新读环境变量，避免 import 早于 load_dotenv。"""
+    debug_val = (os.getenv("DEBUG") or "false").strip().lower()
+    is_dev = debug_val in ("true", "1", "yes", "on")
+    dev = os.getenv("OTA_UPLOAD_DIR_DEV", _OTA_UPLOAD_DIR_DEV_DEFAULT)
+    prod = os.getenv("OTA_UPLOAD_DIR_PROD", _OTA_UPLOAD_DIR_PROD_DEFAULT)
+    raw = dev if is_dev else prod
     return Path(raw)
 
 
diff --git a/backend/routes/ota.py b/backend/routes/ota.py
index 41ddce1..23e210f 100644
--- a/backend/routes/ota.py
+++ b/backend/routes/ota.py
@@ -16,7 +16,7 @@ from ota_storage import (
     upload_x8_package_to_s3,
 )
 
-load_dotenv()
+load_dotenv(override=True)
 
 # Configure logging
 logger = logging.getLogger(__name__)
diff --git a/backend/security.py b/backend/security.py
index 9c4d3ba..fbec419 100644
--- a/backend/security.py
+++ b/backend/security.py
@@ -8,7 +8,7 @@ from dotenv import load_dotenv
 from fastapi import HTTPException, Security
 from fastapi.security import HTTPAuthorizationCredentials, HTTPBearer
 
-load_dotenv()
+load_dotenv(override=True)
 
 logger = logging.getLogger(__name__)