In order to improve the mapping accuracy, a new algorithm is proposed to calibrate optical system distortion when forward image displacement is compensated by driving CCD. The key factors which greatly influence the optics distortion during forward image displacement compensation are researched. Then, by analyzing the effect of principal point and the principal distance on the optical distortion, a mathematical model is established. The model is tested through numerical simulation and field flight experiment. Experimental results show that the mapping accuracy is improved by 1.38 times as compared with the traditional method. The results confirm the feasibility and the validity of the proposed method.