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.