A mechanical model was developed for the four shaft ball lapping machine. The velocity vector of relative machining sphere at one point of the lapping cup was obtained by analyzing the relation between the four lapping cup and machining sphere. The analyzing model for the lapping machine to realize uniform lapping on a ball surface was set up based on Preston equation. And the Matlab software was used to conduct the simulation analysis on unit time deduction.Lapping uniformity was evaluated using variance. When cup turning and reversing is 90°out of phase

the better variance was obtained. In order to obtain lapping uniformity

running direction of four cup must changed.