Abstract: In coal mining, the strike length of the coal working face often reaches several kilometers, so long-distance liquid supply is adopted. The pumping station is several kilometers away from the working face. There is a pressure drop between the outlet pressure of the pumping station and the inlet pressure at the working face. In this paper, Easy5 software is used to simulate various situations of long-distance liquid supply from the working face, and the hydraulic system is simulated and simulated. Thus, the influence of the pipe diameter of the liquid passage pipe on the flow rate of the entire hydraulic system under certain preconditions is obtained. Based on the current design status of the company's hydraulic system and market demand, combined with the actual situation, the most suitable preconditions for the company's products are selected. Then, the pipe diameters of the liquid passage pipes are changed one by one to simulate the hydraulic system, obtaining multiple sets of data. According to the obtained results, the influence of the change items on the flow rate of the entire system is determined, and then the most suitable pipe diameter is selected to ensure that the function of the hydraulic system is not affected. And no excessive design is made. In addition, by changing some other parameters respectively according to the appropriate pipe diameter, the influence of other parameters on the hydraulic system can also be seen, which can further optimize and improve the hydraulic system.