Abstract: The aerators are normally placed at the middle of the first step and the exit of the flaring gate pier, which can effectively reduce the probability of cavitation and scouring damage caused by high-velocity flow to the release structures of high dams. In this study, a water vapor two-phase model with RNG k-εmodeling is used to simulate the aeration on the surface of the stepped spillway and the energy dissipation characteristics; three pre-aerator angles of 8°, 10° and 11.3° are simulated in the energy dissipater of the stepped spillway; VOF method is adopted to deal with the free water surface; and the ways of geometry reconstruction modeling for interpolation, PISO and the unsteady flow methods, which are the numerical simulation methods, are applied. The simulation results indicate that the trend of the aeration concentration is decreasing in general, and the trend stays unchanged at the end of a few steps indifferent angles of the pre-aerators; the step is near and behind an aerated cavity whose tendency of the aeration concentration decreases first and then increases along the concave angle to the lobes on the horizontal step near the wall, while its trend is inverse on the perpendicular step near the wall. In addition, the aeration concentration increases with the enlargement of the pre-aerator angles at the same section; the step is at the ogee section whose aeration concentration increases along the concave angles to the lobes on the horizontal step near the wall; the aeration concentration reduces along the lobes angle to the concave on the perpendicular step near the wall, and the aeration concentration increase with the augment of the pre-aerator angles at the same section. The rates of energy dissipation of the release structure increase with the enlargement of the pre-aerator angles.