Based on energy conservation law, combine with system dynamics, hydromechanics, the mathematical model of the Hoffmann Hydraulic Mechanism (HHM) was established using chamber method. Then, the Ronge-Kutta method was selected to solve the state equations. At last, with the SIMULINK in MATLAB, the system’s dynamic characteristics was analyzed, and the oil pressure changed with time was investigated, both are of direction significance for the system characteristic study and design improving.