Abstract: The working performance of the valve directly affects the performance and safety of the entire pipeline system. In order to build a new type of power system with new energy as the main body, pumped storage technology came to being, which brings great challenges to design of the parameters related to the inlet ball valve of large pump turbine. In this paper, on the premise of not simplifying the valve body structure, the grid-free moving particle simulation method is used to simulate the hydraulic performance of the inlet ball valve of a prototype pump turbine in the process range of the valve full opening from 0 to 90 degree, and the flow filed distribution characteristics in the valve body and inside the pipe of the ball valve, as well as the variation characteristics of the flow resistance coefficient ζ and flow coefficient K_v were summarized. The result show that with the gradual increase of valve opening, the flow resistance coefficient of the ball valve decreases gradually, and the gradient of change is sharply reduced. When the ball valve opening is less than 20 degree, the flow in the return area formed at the upper end of the pipe in the front end of the valve body and the flow in the pipe at the back end of the valve body is insufficient, making the pressure difference between the front and back of the valve body larger, and the flow resistance coefficient exceeds 30.0; When the valve opening is more than 60 degree, the fluid flow in the pipe is stable and smooth, the flow resistance coefficient is lower than 0.15. When the valve opening is about 30 degree, the valve body is subjected to the maximum torque value, and its value reaches 5.6×10⁷N.m. The grid-free moving particle simulation method solves the difficulty of mesh division in the calculation domain of the ball valve body in the traditional Euler method, effectively shortens the hydraulic optimization design cycle of large inlet ball valve. It can enhance the reliability of the design scheme of large inlet ball valve and has certain engineering application value.