Abstract: The study on rock mass parameters after the excavation is always the focus of the engineering.It is the basic work of the rock stability evaluation.This paper is based on the engineering of JinPing Underground Caverns.It classifies the engineering geological rock group about different stake Nos,re-classify the rock mass and evaluation of its quality. It uses the Geological Strength Index(GIS)method and introduces the the number of joint per cubic meter. It can make the evaluation system reasonable. At last the rock mass parameters can be found by regression method. It is found that the calculated values of the cohesion and Internal friction angle are similar to the recommended values.This method is relatively easy. It can provide reference for the selection of mechanical parameters of other underground excavation engineering with similar geological conditions.