In the discharge structure, in order to prevent flowing interface from being destroyed by cavitation under high speed velocity, aerator was introduced to concave reach bottom. Engineering practice and scientific research showed that backwater appeared in the cavity to reduce the effective cavity length and the aerated result was not good under the condition of a small slope after aerator. Through numerical simulation and model test，aerator arrangement was studied. The results showed that while adopting aerator on the bottom of concave section，adding the centrifugal would remarkably influence on the length of bottom cavity; Introducing lengthen section on the bottom of concave reach，the additional centrifugal force had transition nature after the tangential point; With the reducing of adding centrifugal，the length of bottom cavity obviously increased; When the length ratio of lengthen section and concave lengthwas in 0.16，the bottom cavity length obviously increased，and the hydraulic characteristic got certain improvement.
