Kinematic characteristic of wafer driving initiatively in plane lapping process was analysised based on the model of lapping geometry. A new rule was deduced for evaluate the uniformity of lapping trajectory by trajectory numbers of each unit wafer area. The effects of rotating ratio and eccentricity on the uniformity of the lapping trajectory were theoretically analysed. Lower eccentricity is helpful to improve the trajectory uniform distribution, for the errors of the relative rotating speed are augmented with large eccentricity. Forever, improvement of rotating ratio is also to enlarge the standard deviation of trajectory points in the same area, and make a bad uniformity. The same angular velocity for lapping plate as wafer is recommended to improve the trajectory uniformity.