Abstract: To determine the parameters of gear profile modification accurately, the effect of transmission error on gear vibration was analyzed to simulate the meshing process of a pair of gears via FEM. With the GA(genetic algorithm) introduced into the process to reduce the fluctuation of transmission error, the profile modification parameters of spur gears were designed optimally and accurately. The results showed that the gear profile modification parameters thus given are so accurate and efficient that the impact on gear meshing can be avoided with the dynamic fluctuation of transmission error of spur gears decreased greatly. A new way to the R&D and design of noiseless gears is thus proposed.