Electrohydraulic servo valves can be divided into flow servo valves and pressure servo valves according to functions, pressure servo valves are commonly used in force application systems, and flow servo valves are more widely used in force system or position system. In high stiffness load system, the commonly used flow servo valve can not meet the requirements of the system, pressure electrohydraulic servo valve is generally needed. The singlestage pressure servo valve, twostage semiopenloop pressure servo valve, twostage closedloop pressure servo valve and direct drive pressure servo valve were introduced, the characteristics, advantages and disadvantages of each type of pressure servo valve were described.