According to the subgrade test devices hydraulic principle diagram, the dynamic pressure cylinder electrohydraulic 〖JP2〗servo pressure system transfer function and AMESim model are established. The transfer function was divided into three parts of the servo〖JP〗 valve system, the load dynamic pressure cylinder and the flow nonlinearity. The identification model and algorithm used were introduced, and an identification scheme based on the AMESim model was designed to obtain the open loop transfer function parameters of the servo valve system and the load dynamic pressure cylinder. At last, through contrast simulation, this methods validity is verified.