Taking the gear transmission mechanism of a five-gear transmission as the research object,the simulation model of the gear transmission mechanism of the transmission is established by using Romax Designer software,and the load-bearing situation,transmission error and load distribution on the tooth surface of the 4 th gear are simulated and analyzed. According to the theory of tooth lead modification and tooth profile modification,the variable range of three-dimensional modification parameters of the 4 th gear is analyzed by orthogonal experiment principle. Then the genetic algorithm is used to optimize the modification parameters of gear,and the optimal combination of modification parameters is obtained. The validity of this method is verified by vehicle test. By comparing the results before and after optimization,it can be seen that the three-dimensional gear modification technology can greatly reduce the stress of the gear,reduce the fluctuation amplitude of the transmission error of the gear,optimize the stress distribution of the gear tooth surface,and reduce the vibration noise. At the same time,it can be proved that this method can effectively improve the meshing condition of gears and is an effective means to optimize the meshing performance of gears.