A two degrees-of-freedom vehicle dynamic and a tyre model were discussed to overcome the low precision of the traditional vehicle steering system modeling and simulation. Then an electric power steering system（EPS） hardware-in-loop simulation test platform using two servo motors was developed. EPS steering angle can be input by either hand or input servo motor, while the output servo motor can dynamically simulate the real vehicle steering resistance torque according to the solutions of vehicle dynamic and tyre model under current steering angle and realvehicle operating parameters. Thus the EPS can be evaluated and debugged by detecting and checking critical signals. Test results show that the simulation test platform has good real-time and reliable character istic as well as high simulation precision, and can correctly catch the critical EPS performance parameters, so it is very suitable for developing, testing and evaluating EPS．