Abstract: The left bank foundation of one hydropower station upstream is on bedrock,the right bank foundation is on the loosening body.The upstream overburn layer is devided into three kinds of rocks.The I and III rock layer are the strong leakage layers,and the II layer is medium leakage layer.Central dam circle leakage will appear after retaining the water of cofferdam.To calculate the three-dimensional finite element of the upstream cofferdam and foundation in order to solve the problems of anti-seepage and dam circle leakage of upstream cofferdam and choose the optimum plan.The calculation shows that we must build the concrete anti-seepage wall of the river body overburn layer.According to the real terrain condition and the difficulty of construction,we optimize the anti-seepage plan to the loosening body of the right river bank and decide to choose the anti-seepage curtain to prevent the seepage of the loosening body.