Abstract：Based on the comprehensive analysis of geological conditions and deformation monitoring，the simplified geological model and excavation model of the experimental cavity are set up. The assumption of linear distribution of in-situ stresses of rock masses along depth is adopted，and based on the in-situ stress measurement，the interval of in-situ stresses is decided for back analysis. Then，the uniform design method and FLAC3D are used to make back-analysis on in-situ stress field of the underground powerhouse area of Longtan Hydropower Station through simulating the excavation of the experimental cavity by steps. 12 excavation cases are selected for simulation. The displacement object function values are calculated for each case by steps. The minimization of object function is made，and the distribution regularity of in-situ stresses of rock masses along depth is obtained. By comparison of measured and calculated displacements and in-situ stresses of rock masses，it is shown that the obtained results are satisfactory and the presented back analysis is reasonable and effective.
