The vehicle simulation model for a certain car was set up using the GT-DRIVE software which is often used to simulate the vehicle performance.Based on the simulation results of the new European driving cycle (NEDC),the influences of transmissions with different gear numbers on vehicle economy and emissions were analyzed.The Latin hypercube sampling method (LHS) was adopted for the design of experiment (DOE) about the final drive ratio and various gear ratios.By the regression analysis,three parameters that have significant effects on the automobile economy and emissions were determined,and the laws of their influences were studied.Finally,the strategy of combining DOE and genetic algorithm (GA) was applied to achieve optimal design.The objective of improving economy and emission performance on the premise of ensuring the dynamic performance is attained.