Based on the analysis of tralipump hydraulic system, the mathematical model of trailer pump hydraulic system was established using the power bond graph theory.And the mathematical model of the hydraulic system was simulated using the dynamic analysis software package of MATLAB/Simulink.The results show that the simulation model is accurate.It can be used to analysis the key parameters of system without doing more experiments on the prototype.So it saves a lot of time, and to avoid the risk of unsuitable parameter of experiments.Meanwhile,the method can set a referance for design,analysis and optimization on the hydraulic circuit system of other construction machinery.