Abstract: Based on the characteristic of tooth profile modification,the method of three segment modification for pinion profile was presented.Through changing the shape of cutter-edge,three-segment parabola was used to substitute for the linear profile,and cutter surface equation was deduced.Coordinate system for double helical gears meshing was built,and furthermore,tooth contact analysis and loaded contact analysis was proposed.By taking least transmission error as optimization goal and the optimization parameters were obtained by applying complex method.A case study shows that,in the case of axes error,the optimization results of profile and axial modification without consideration of axes error can still obviously reduce the loaded transmission error compared with no modification optimization.Finally,the calculation method of pinion profile modification was given.