Initial stress is one of the key factors influencing stability of slope，underground cavity and foundation rock mass，and is one of the elementary indexes required in engineering design，especially in large hydroelectric engineering. By using 3-D elastoplasticity FEM，the initial stress field in a large hydropower project on Jinsha River is simulated and fitted. The result shows that the calculations fit well with in-situ measuring data and can satisfy design need. The fitting is better for than that for .