Billet is designed by utilizing the flow relief-hole principle to improve the dimensional accuracy during the precision cold forging of helical gear . An optimization method for the initial diameter of the relief-hole was proposed based on the finite element method(FEM) and response surface method (RSM). The degree of uniformity of effective strain in helical gear precision forging was considered as the optimal objective. The empirical equation built through Response Surface Method shows the relationship between the the initial diameter of the relief-hole and the degree of uniformity of effective strain. The optimal diameter is obtained through gold section method based on the empirical equation . The optimal result has been verified by using the commercial software DEFORM 3D.