Abstract: The three-dimensional flow field of the integrated valve step-down flow channel was studied with the computational fluid dynamics (CFD) program CFX. The calculated hydraulic characteristic results of the flow channel agree well with the results of the integrated valve step-down flow channel flow resistance experiment, which validates the reliability of the numerical model. On the basis of the numerical simulation results, the velocity and pressure distribution schemes inside the flow field were analyzed. The research results indicate that the flow velocity reaches its peak value at the upper side of the valve core entrance flow channel, the flow velocity is uniformly distributed inside the returning water cavity of the integrated valve flow channel, the maximum pressure head loss occurs at the intersection area between the horizontal and vertical valve inlet channels, and measures such as increasing the channel diameter or adding a curving transitional channel can be adopted to reduce the pressure loss.