Abstract: Geba Reservoir in Guizhou Province is a masonry single curvature arch dam. At present, there are some problems in the dam top spillway, such as insufficient flood discharge capacity, unstable overflow tongue in the surface outlet, obvious vibration of the dam body during flood discharge, etc. In the course of danger removal and reinforcement of the reservoir, the overflow weir body has been rebuilt, and the downstream dam surface has been thickened to lift the check flood water level and increase the flood discharge capacity. It is believed that thinner overflow weir should be adopted in arch dam, so three kinds of curved practical weir, such as WES type, Changyan I type and CO type, were studied and compared through experiments. Finally, the WES type weir was selected, which is the thinnest and is convenient for construction lofting. After the rebuilt of the overflow weir, the negative pressure of the water tongue on the weir surface was eliminated by eliminating water tongue detaching from the dam surface, and no vibration of the dam body was found during flood discharge. At the same time, in order to meet the atomization influence and flood control standard at downstream of the dam, the following joint energy dissipation schemes were selected: flip bucket with negative angle, riverbed apron and baffle block, which solved the problems of atomization, water tongue scouring and flood control of power plant.