Abstract: Using the infiltration upper-edge-line by the existing methods in the numerical simulation of the 3-D seepage field，the larger errors of the numerical results would be caused compared by the testing results.According to this problems，a new indirect conversion method is presented to determine the more accurate location of the infiltration upper-edge-line.Based on the seepage theory and the finite element method，the numerical simulation is carried out to analyze the 3-D seepage field by selecting three different location of the infiltration upper-udge-lines.And the numerical results are compared with the testing results，which shows the validity of the method presented in the paper to accurately determine the infiltration upper-edge-line in the numerical simulation.

Key words: Tailings reservoir, 3-D seepage field, Infiltration upper-edge-line, Dry beach length, Saturated surface