Take relief valve of mine water hydraulic threefunction valve as the research object. Through computational fluid dynamics(CFD) twophase flow technology, contrast analysis of cavitation characteristics of slide valve type relief valve and needle type relief valve, study the pressure and cavitation distribution, and analysis influence of size of the relief valve structure on improving cavitation damage were carried out. And the slide valve relief valve of flow angle was optimized to further reduce the occurrence of cavitation phenomenon. Results show that: Relative to the needle valve type relief valve, slide valve type relief valve of cavitation damage is small. When the slide valve type relief valve of flow angleα=45°, the valve cavity cavitation intensity is minimum, cavitation area is minimum, and the maximum gas phase volume fraction is only 24.5% in the important valve mouth. After optimization of the relief valve can effectively restrain cavitation, improve safety performance and service life of the relief valve.