The lapping trace distribution on ball surface is one of the key factors during the lapping process, which can affect the sphericity of lapping. The Rotated Dual-Plates lapping mode (RDP lapping mode) can achieve better uniformity of lapping trace distribution on precision ball surface, which ensure the results of forming sphere by lapping. Combining with the basic principle of RDP lapping mode, as well as the analysis of the kinematics of the RDP lapping method, this paper puts forward a basic rule about the material removal at the contact point between the ball and the plate with the material removal rate equation of bearing steel, and the improvement of the sphericity which can be simulated, and is defined as the lapping uniformity according to basic rule equation. The influence caused by the lapping pressure and the speed of the plates are considered in the simulation, the surface of ball is triangle grid divided. The uniformity of lapping is evaluated at different speed ratio, and eventually a better curve of the speed ratio can be got, so the lapping uniformity during the RDP lapping mode can finally be accurately evaluated.