Based on the analysis of the transmission errors and the effect contact ratio under lapping, the mean boundaries of the lapping contact of tooth surface are determined and the lapping paths are schemed. The relative lapping rate of the tooth surface is estimated by means of the synthesis of the sliding coefficient, the lapping probability and the dynamic lapping force. The mechanism of the tooth flank modification on the errors corrected mutually and averaged dynamically in the lapping process are presented and investigated. The teeth precision and the dynamic mesh behavior before the lapping have been compared with these after lapping, the results of which show that the lapping may reduce the teeth form errors and spacing variations to some extent and improve greatly the teeth meshing precision and the dynamic mesh behavior.