The theory of the excavator’s hydraulic system was elaborated in the paper taking a 20t hybrid hydraulic excavator produced by a domestic company for example. The rotary movement of the hybrid hydraulic excavator was achieved by a newly developed electric motor, fuel consumption could be reduced as the result of the speed inhibition when the excavator standby. The modeling of excavator’s hydraulic system, front-end attachments and revolving frame were built on the AMESim platform according to the installation and actual sizes of the hydraulic components. By setting the parameters of every component in the model, mechanical- electronic- hydraulic integrated simulation was achieved. The paper focused on the solutions of hydraulic system’s pressure fluctuation and poor simulation results of front-end attachments. As a conclusion, appropriate solutions and simulation results were proposed to improve the precision.