Load distribution of the flexspline under alternating dynamic loads is complicated, and it’s difficult to measure the stress of the flexspline by experiment. To study the intensity of the flexspline, operating process of a harmonic drive is simulated based on the contact theory and the explicit algorithm of the finite element method. The parameterized finite element grid of the whole harmonic drive model is realized by Matlab, and then the assembly process of the vave generator is simulated by ABAQUS. Meanwhile, the distribution of the flexspline stress and the load characteristics of the flexspline tooth during dynamic transmission process of a harmonic drive are analyzed. The fatigue fracture position on the flexspline is forecasted according to the simulation results at last.