Taking the piston pump and high speed on-off valve, the crucial parts of automotive electronic stability program (ESP). Their mathematical models were established. Besides, the co-simulation model of ESP hydraulic control unit (HCU) was built up by AMESim and Matlab, which was also verified by test. The simulation model described the motion intrinsic characteristic of the piston pump and high speed on-off valve. Consequently, the effect of those components’ parameters on the adjustment of braking pressure during active boosting was analyzed. The result can provide references for the design and development of ESP, especially for improving the efficiency of the pump and the linear control performance of the high speed on-off valve. 