Abstract: Based on the principle of the hydraulic system of signal producer controlled by on-off pilot valve, and according to the different working characteristic of three phases,using the liquid flow and pressure characteristic of valve, the dynamic equilibrium equations for flow flux of every subsystem are established; By taking account of the steady and instantaneous hydraulic impetus, the main and overflow valve’s dynamic equilibrium equations of force in every phases are established; Farther more, by choosing the pilot valve’s opening degree and import flow flux as the control variables, by choosing the main and overflow valve’s opening degree and velocity as the variables of state, the nonlinear equations of state of three phases are presented, and a simulating calculation of practical example has been conducted.