In this paper, the MEMS-based IMU (Inertial Measurement Unit) was used in a fusion navigation system comprising a MEMS-based IMU and a GPS device with the map database. The attitude angle of a vehicle at a specific location is detected by the MEMS-based IMU and compared with the identifying information from the map database for judging whether the vehicle is on a correct route or not. The fusion navigation system generates a navigation route in accordance with the start and destination and determines whether the attitude angle is conformed to the identifying information from the map database with respect to the specific location on the navigation route. If the attitude angle is not conformed to the identifying information, the navigation route for the vehicle could be modified immediately. This method could help the GPS device to determine whether the vehicle is traveling on the viaduct bridge or on the surface road and whether a driver of the vehicle had taken a route other than the navigation route at the first instant, and thus modifying the navigation route according to the comparison for guiding the driving on a correct route to the destination specified in the navigation information.