Abstract: Based on the FEM for steady seepage,and combining with the analyse of parametric sensitivity and the objective function in optimal design,the construction schedule was taken as the objective function and the overflow hydraulic gradient and the construction time as the restrictive conditions,the optimization of depth of suspended anti-seepage wall in the cofferdam of a hydraulic power station in the Dadu River was performed.Variation of some sensitive parameters including the hydraulic gradient and the schedule with depth of suspended anti-seepage wall was analyzed,and the relationship among them was obtained through the normalization of thinking.The anti-seepage depth was obtained through the restraint condition,and the optimized depth was then yielded.The results were not only necessary for the economy and safety of the engineering construction,but also reasonable for the theorietical basis of the evaluation to suspended cut-off walls.