Abstract: Sufficient flow aeration could relieve cavitation erosion of high-velocity flood releasing facilities, and also change their relative hydraulic characteristics. We carried out hydraulic model tests to the tunnel spillway aeration facilities of a dam and relative analysis on the occurrence conditions of free flow self-aeration, and based on the results we proposed to set only one level aeration facilities in the free flow tunnels with a length of 550m and velocity over 38m/s in the whole length, which could reduce two level aeration facilities compared to conventional projects. Aiming at the feature that the angle between the out-flow direction and river direction reaches up to 60°, a heterogenic energy dissipation bucket lip with large differential was put forward. The model tests showed that this energy dissipater makes the nappe spread well along the longitude direction, and nappe outer edge keeps a safe distance of more than 30 m from the opposite bank. After longtime operation of the tunnel spillway under high water head since its completion, there was no cavitation erosion appeared on its free flow tunnel and energy dissipation bucket lip, but the nappe washed against the opposite bank.