Abstract: Based on instruction of the structure of hydraulic net, the mathematical model of the subsystem with hydraulic transformer and accumulator in series is established. Then，two arithmetic to control the pressure of system according to load flow and the pressure of system respectively are put forward. After analyzed the shortcoming of the former, a nonlinear control equation is educed. The result of the control equation and simulation proves feasibility of the second control method.

Key words: Equation for pressure control, Hydraulic net with constant pressure, Hydraulic transformer