Abstract: Using a pre-aerator to connect WES curved surface with the stepped spillway in an integrative energy dissipater combination which includes flaring gate pier, stepped spillway and stilling basin can effectively increase the stepped surface aeration and protect stepped spillway from cavitation. The authors of this paper have utilized a RNG k-ε turbulence model and a water-vapor VOF model, made geometry reconstruction for interpolation, and used PISO and an unsteady algorithm to simulate the aerated cavity length and pressure distribution of the stepped spillway under the conditions of different pre-aerator angles of 8°, 10° and 11.3°; the simulation range is from the upstream reservoir to the downstream stilling basin. In order to verify the reliability of the numerical simulation, the model experiment of the stepped spillway for the aerated cavity was conducted. From analysis and comparison of the measured values and the simulated values of the aerated carity length, it is found that there is a small deviation between both values, and the maximum error is 7.9%. The numerical simulation results indicate that the aerated cavity length increases with the enlargement of the pre-aerator angle; the absolute values of the maximum negative pressures and shock pressures of the stepped surface increase with the augment of the pre-aerator angles; and the range of the negative pressure distribution is expanding gradually.