Abstract: The moving speed can cause the target image to disperse in the vehicle-mounted forward-looking virtual aperture radar using stepped frequency and it could heavily infect image feature extraction of target. In this paper, the influence on imaging introduced by vehicle moving is analyzed basing on an ideal point model, and then the equivalent principle of speed compensating is brought forward. Basing on the analyses discussed upon, a new method of speed compensation, which will make the compactness of the Range Of Interest (ROI) image optimal, is introduced. This method can not only enhance the speed compensation efficiency, but also improve the stability of the feature extraction. Both the simulation data and the practical data prove the effectiveness of the method mentioned above.