It is well known that the effect of air entrainment for cavitation damage controls is related not only to the air discharge into aerator devices but also the flow regime of the cavity below them.On the basis of the hydraulic characteristics of the flow,the aerator devices were for the first time classified.The theoretical considerations were performed about the jet length and cavity flow regime with the influencing factors.Comparing with the behavior of the flow through the aerator of discharge tunnels,the flow regimes of the cavity below spillway aerators were experimentally investigated,and the empirical expressions were presented to identify the conversions of the cavity flow regimes,including fully filled cavity,partially filled cavity,and net air cavity.Some issues of the design of the aerator devices were suggested in the present work. It is well known that the effect of air entrainment for cavitation damage controls is related not only to air not into aerator devices but also the flow regime of the cavity below them. On the basis of the hydraulic characteristics of the flow, the aerator devices were for the first time classified the theore considerations previously performed about the jet length and cavity flow regime with the influencing factors. Comparing with the behavior of the flow through the aerator of discharge tunnels, the flow regimes of the cavity below spillway aerators were experimentally investigated, and the empirical expressions were presented to identify the conversions of the cavity flow regimes, including fully filled cavities, partially filled cavities, and net air cavities. Some issues of the design of the aerator devices were suggested in the present work.