Initial stress is one of the key factors for rock engineering

and is one of the elementary indexes required in design

especially for large hydroelectric engineering. The study on in-situ stress field of rock mass around the dam area of Baihetan Hydropower Station had been carried out. Based on the means of numerical simulation with three-dimensional distinct element code (3DEC)

the rock mass natural stress of a valley has been simulated. The result shows that the stress distribution has three areas: the area of loosed stress

the area of concentrated stress and the area of stable stress

which is according with typical stress distribution pattern in a deep valley. What is more

the calculations fit well with in-situ measuring data by using hydraulic fracturing method including 6 points. The simulation results delineate clearly the whole outline of the stress field of dam site

and provide important basis for analysis and design.