Precision planetary reducer has the advantages of high transmission precision and high efficiency.Its performance has an important impact on the overall performance of the application system.In order to improve the transmission performance of the precision planetary reducer,taking the two-stage precision planetary reducer as an example,the 3D model of the two-stage precision planetary reducer was established,the combined modification method of helix with drum shape was used for optimal design,the gear contact characteristics of the overall gear train of the two-stage precision planetary reducer were analyzed,and the contact characteristics of the reducer before and after modification were compared and analyzed.The analysis results show that the helix modification with drum shape can obtain the optimal solution quickly and iteratively,and reduce the transmission error of the reducer and the tooth surface contact stress concentration caused by meshing deformation.