Because of driving experience and comfort of electric vehicle， the working performance of its dive system must be well in the diving process. Structural analysis and dynamical system calculating of a two speed transmission are carried out， which based on a certain type of electric vehicle， and the flexible simulation model of the transmission system is designed and established based on Adams/View platform. The dive speed of electromotor in different gears is constructed by using Step function， and in the simulation conditions of 0~50 km/h and 50~80 km/h speed range， the kinematics characteristics and impact load on axle head which under first gear and second gear are calculated， analyzed and compared， on the basis of the results， the driving transfer process and variable speed performance of the transmission are verified. The dynamics optimization of input axis is carried out by modal analysis and zero order optimization algorithm， and then dynamic stability of the transmission system is enhanced effectively. All of above provide some technical reference for dynamic design and performance study of new energy vehicle transmission system.