An approach based on the minimum amplitude of loaded transmission error, meshing impact force and acceleration of vibration with drive diagonal modified helical gears was proposed to reduce vibration and noise. Firstly, the modified tooth surfaces was represented by a sum of two vector functions that determined the theoretical tooth surface and the deviations surface, which was fitted by 3 B Spline based on tooth surface grid data established by the deviation curve. Secondly, with the tooth bearing deformation ascertained by TCA and LTCA, the meshing force and meshing stiffness were established according to the meshing impact theory. Finally, a dynamic model with a pair of helical gear was built, and used genetic algorithm to optimize the parameter of curve to get the best deviation surface. The results shows that the diagonal modified helical gears can greatly reduce the vibration and noise due to the positions changing and small loads under approaching meshing, as well as higher coincidence degree than other type modified gears.