Considering the gravity and tectonic stress as the ma in factors of in -situ stress of rock mass, a multivariate re gression method，based on 3 -D FEM direct modeling，is summar ized. The method is applied to Shenzhen Pumped Storage Power Plant, the regressi on coefficients corresponding to the in -situ stress factors are determined by fitting the stress measured values, and the initial stress fie ld is obtained for the rock mass of whole engineering. 