Abstract: Two speed-precision measurement methods, real-time and quasi-real-time method, are described. For real-time method, the real-values of COG and SOG are got from DGPS. For quasi-real-time method, the real-values of COG and SOG are calculated by Mid-Latitude, Mercator or Bowring sailing method, the geographic coordinates obtained from DGPS are taken as the original datum of the three sailing methods. The bearings used by both two method are got from platform-gyrocompass.