Abstract: Based on research of the design program of excavating another drainage corridor in the dam,two kinds of 3-dimensional static seepage algorithm,the loosen method and the abandoned element method,are given and compared them with analytic solution.Then the abandoned element method is used to research the seepage finite elemenx of the dam of Fongmeng.The conclusion is that it can lower the frozen point at lower reaches for excavating another drainage corridor.The result of strength analysis shows that the program putting into practice'vtill not influent the safety reliability of the dam.