Abstract:AMESim software was used to build the mathematical model of jet pipe type electrohydraulic servo valve. The pressure characteristic curve was obtained when the brake chamber was connected with brake disc or not. The effectiveness of the simulation model was verified by experiments.When the control chamber was very small, the movement of the spool of the pressure servo valve was characterized by high frequency vibration. At the same time, the characteristics at the jumping and falling point of the pressure characteristic curve were obtained, which was related to the volume of the brake disc cavity, the spring stiffness and the pretightening force.