In this paper, the slope stability problem of phosphate gypsum dam with steady seepage is analyzed, and the parameter study is carried out with finite element software ABAQUS. By editing the Python script file, the strength reduction FEM method is realized in ABAQUS through parameter study, which has the characteristic of finding the slope surface automatically. In this way the slope stability with steady seepage is studied. In accordance with the seepage field obtained by the above method, a new method which sets drainage body between first dam and phosphate gypsum dam is presented, and the calculated result shows that this measure can reduce the location of phreatic surface of seepage field of dam greatly, meanwhile the slope stability is improved. The disposal of new drainage system is cheap so it has practical engineering significance.