In order to analyze dynamic characteristic accurately during steering, electric power steering system is selected as research object and dynamic equation of steering system is established. Combined with eleven degrees of freedom vehicle model and tire model at combined conditions of longitudinal slip and side slip, the integral-simulation model of electric power steering system is established. The dynamic response of steering system at different steering wheel angle, control methods, front wheel steering angle and braking force is analyzed. The simulation results show that electric power steering system with neural network control has good stability, tracking performance, assist characteristic and anti-interference ability. The established model can reflect the dynamic characteristic correctly and effectively during steering.