Abstract: In the article ,the authors mainly study and calculate a significant engineering problem about water leakage in left dam abutment of Heihe Reservoir. A three-dimensional finite difference method is used to simulate seepage flow under natural conditions and high hydraulic head was simulated, the way of percolation was analyze and the quantity of leakage at left dam abutment of Heihe Reservoir was calculated. A fact that the fault became a conduit for intensive percolation is verified by the calculation. Then according to hydraulic head, using three-dimension finite-difference method, we calculate water table and the stability of slope at left dam abutment is studied and analyzed by using limit equilibrium analysis method. All the results are of important referential value for the decision -making and design of practical engineering project.