Circular-scanning SAR is mainly used for scene matching in the precision-guide d mi ssiles, whe r e the motion parameters of radar are one of the key factors to achieve precision - guided. Motion parameters can be directly measured by the GPS and MIU, and also c an be estimated from the measured data. The characteristics of fast velocity,non uniform motion and big strabismus of the circular scanning SAR platform requi re high quality of the SAR image. But the motion parameters measured by the GPS and radar IMU are difficult to meet the accuracy requirements since the large e r rors of motion parameters. By combining the two parameter estimations, accurate estimation and motion compensation are performed for the motion parameters in or der to meet the req uirements of high-resolution images and precision guided.The simulation result s verify the validity of the proposed scheme by improving the quality of circula r-scanning SAR image. The results of measured data prove that the scheme is ver y practical.