Abstract: Time stepping FEM method being used to analyze transient process of generator has great significance of improving system stability analysis for generator. In this paper, field circuit coupling time stepping FEM method is adopted to establish dynamic simulation model of synchronous generator, and three phase sudden short circuit for a 7.5kW nonlinear generator is simulated. The transient currents acquired by simulation and experiment are decomposed using Prony method, and AC/DC components are obtained. The validity of this dynamic simulation model is verified by comparable analysis, and time constant T_a and T′_d are identified as well. Then, through the simulation of load sudden short circuit under different exciting currents, the trend of different responses can be obtained.