A method to improve the dynamic characteristics of gear system is proposed through the selection of spiral angle of helical gear according to gear system dynamics theory.Based on the finite element theory

the laws of tooth load distribution in long direction and load distribution between tooth and the expression of gear parameters and tooth load through the comparison with the variation laws of contact wire of gear tooth in meshing process are obtained.Then

the calculation formula for optimal helix angle of helical gear regarding the variation laws of contact wire least as the target function are deduced

and the formula correctness through the comparison of the meshing stiffness of different helix angle is proved.The results provided theoretical base for the optimization of design parameter of helical gear.