The coupled seepage and safety factors are calculated in some homogeneous dam in Xi ' an City under the following four boundary conditions, i.e. not setting vertical boundaries, setting a permeable boundary, adding an infinite boundary and instituting both infinite and permeable condition. The slope stability is analyzed with slope calculation considering seepage. The calculated result shows that it is not coincident with the measured data under the infinite boundary condition, while that it is in accordance with the measured data under permeable boundary condition. The conclusion could provide a reference in setting the boundary condition.