To investigate the steering characteristics of the hydraulic power steering system, a Modelica-based modeling approach is proposed. An automobile steering system test bench is set up for parameters identification. System characteristic features such as transmission ratio, stiffness, viscous damping and dry friction are estimated by bench test. The full version of hydraulic power steering system model is established in Dymola platform. For the sake of validating the proposed model, the vehicle steering performances are measured in field experiments which test maneuvers include the parking-lot steering and the lemniscate-shape path following. By driving the model with steering wheel angle signals measured in tests, the simulation results provide estimated performance of the hydraulic power steering system. The comparison between simulation and experiment results demonstrate the feasibility of proposed approach.