To improve the performance of battery electric vehicle gear transmission over the entire range of operating conditions, a tooth surface modification method considering the influence of load torque and speed is proposed. The system dynamics analysis model is established considering timevarying meshing stiffness, meshing impact and tooth surface friction excitation. Combined with Tooth Contact Analysis (TCA) and Loaded Tooth Contact Analysis (LTCA), the optimal tooth profile and axial parabolic modification coefficient are obtained by genetic algorithm optimization for full working conditions. The vibration suppression effects of different modification schemes are compared and analyzed. Simulation results show that the root mean square of vibration acceleration of the tooth surface modification, that considering the influence of working conditions, remains at a low level under full working conditions, indicating that this strategy of tooth surface modification has better global vibration suppression effect.