By using the standard k-ε model to simulate turbulence and VOF method to track the free surface of Alagou spillway at different flow rates of three-dimensional flow field numerical simulation. And the design flood level and check flood level under two kinds of conditions, the free water surface and bottom pressure, velocity and the model test observation data were compared and analyzed; the results show that the numerical simulation results and measured data are basically consistent, witch can provide the reliable basis for Alagou reservoir spillway optimization design.