Automotive transmission is one of the key components of automotive, and the design quality of transmission can affect the driving performance, fuel consumption and serve life of vehicle greatly, therefore it is very important to design planetary transmission of vehicle. Genetic algorithm can seek parallelized different regions of the whole parameter space in the progress of its replacement, and make a progress towards being possible to find optimum global solution. The planetary transmission is designed by the minimum volume of objective optimization, and considering loading property and material quality, the constraints are set up. Combination of genetic algorithm and SQP is adopted to solve optimization model. So the AMT have a more compact structure. and vehicle passing performance can be improved and vehicle equipment mass be reduced.