Abstract: After the water stotage of the reservoir, underground stress field, strain field and flow field are formed in a certain spatial range. A mathematical-mechanical model is set up to describe the characteristics of hydraulic pressure stress field. By applying the NOLM83 two-dimensional finite-element program for non-linear stress-strain and stability static force analysis of elastic-plastic rock-soil system, we find that the maximum principal stress of the reservoirs hydraulic pressure stress field decreases gradually from the center of the reservoir to its both sides and from the surface to the depth. The stress, strain, and the range of the Shuitianba fault affected by future hydraulic pressure stress at the reservoir are further studied. The result shows that the affected range in plane is about 5～6 km at the both sides of the fault. Due to the floating effect of rock mass, the cumulative displacement of the surface is less than 10 mm and decreases downwards. Therefore, the fault can fully withstand the hydraulic pressure stress induced by the water storage of the reservoir, and will not affect the safety of the ThreeGorges project since no moderate-strong reservoir-induced earthquake will occur.