Abstract: In the flat planetary lapping process, the lapping quality of optical lens has close relation with the uniformity of abrasion of lapping plate. In this paper, the motion law of optical lens in the flat planetary lapping process was analyzed. The model of lens motion trajectory and lens motion velocity in the conditions of differential gear trains was set up. Besides, the simulation program was developed with Matlab software. In addition, combined with the actual production process, the lens motion trajectory and lens motion velocity were simulated in the conditions of planetary gear train. The influence law of lapping machine speed ratio on the uniformity of abrasion of lapping plate was confirmed. When the speed radio I1-1.5, the lapping plate is covered by the lens motion trajectory in short time and the abrasion of lapping plate is uniform. Therefore, the lapping process has better quality and higher efficiency than before. Finally, the high quality optical lens, which consistency of lens thickness was better than 0.002 mm and parallelism was better than 0.002 mm, was obtained by optimized process parameters based on the simulation result.