diff --git a/hgdriver/hgdev/usb_manager.cpp b/hgdriver/hgdev/usb_manager.cpp
index efb385f..887fd76 100644
--- a/hgdriver/hgdev/usb_manager.cpp
+++ b/hgdriver/hgdev/usb_manager.cpp
@@ -70,7 +70,7 @@ int LIBUSB_CALL usb_manager::usb_pnp_callback(libusb_context* ctx, libusb_device
     usb_manager* obj = (usb_manager*)monitor;
 
 //    if (event == LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED)
-        libusb_ref_device(device);  // keep the object until handle it
+        //libusb_ref_device(device);  // keep the object until handle it
     //else if(event == LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT)
     //    libusb_unref_device(device);
 
@@ -187,17 +187,22 @@ void usb_manager::thread_notify_usb_event()
                 }
             }
 
+            libusb_ref_device(pd.dev);      // for re-enter the queue pnp_events_
             notify_usb_event(pd, &retry);
             if (retry)
             {
-                if(std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::system_clock::now() - pd.happen_time).count()
+                if (std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::system_clock::now() - pd.happen_time).count()
                     <= 5000)
                     pnp_events_.Put(pd, sizeof(pd));
+                else
+                    retry = false;
                 if(pnp_events_.Size() == 1)
                     this_thread::sleep_for(chrono::milliseconds(1000));
                 else
                     this_thread::sleep_for(chrono::milliseconds(delay));
             }
+            if (!retry)
+                libusb_unref_device(pd.dev);
         }
     }
 }
@@ -283,6 +288,7 @@ int usb_manager::on_usb_pnp_event(libusb_context *ctx, libusb_device *device, li
     PNPDEV pd;
     unsigned ms = std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::system_clock::now() - born_).count();
 
+    libusb_ref_device(device);
     pd.ctx = ctx;
     pd.dev = device;
     pd.event = event;
@@ -295,9 +301,12 @@ int usb_manager::on_usb_pnp_event(libusb_context *ctx, libusb_device *device, li
     else
     {
         bool retry = false;
+        libusb_ref_device(device);
         notify_usb_event(pd, &retry);
         if(retry)
             pnp_events_.Put(pd, sizeof(pd));
+        else
+            libusb_unref_device(device);
     }
 
     return 0;