To prevent cavitation damage of hydraulic structures with high speed flows，forced aeration device is commonly adopted as an economical and effective engineering technique. During engineering protecting of the side walls with high speed flows and low pressure areas tend to be neglected. In paper based on theoretic study and model experiment，preventing cavitation damage of the dragon raise head spillway tunnel side walls was studied，an aerator with a sudden widen（ie. lateral deflector）and a vertical drop was put forward to bottom of anti-arc. This type aerator eliminates un-airflow area in the side-walls. The air entrainment quantity is obviously affected by lateral deflector. The lateral air chamber is an important aeration mechanism when the lateral air chamber is connected to the bottom cavity，which prevent cavitation damage of sidewalls and soleplates effectively.
