Dam foundation seepage of reservoir induces the loss of reservoir storage, but more important, it causes dam seepage stability and deformation. This paper used numerical simulation of 3-D groundwater flow to calculate seepage quantity and analyze seepage stability, which has solved the problem of surrounding, bottom boundary of irregular and heterogeneity on vertical sequence well. Meanwhile, the calculation accuracy was enhanced. This study was applied to the Wayan Reservoir in Qinghai Provence. According to the hydrogeological char acteristics of dam foundation，a model for the three -dimensional numerical simulation of flow was established to solve the seepage problem of this reservoir. To evaluate the seepage stability of dam, this paper analyzed the leakage quantity and hydraulic gradient of egress section in conditions of different depth of impermeable wall. The results show that the dam foundation of Wayan Reservoir is in the steady seepage state, when the depth of antiseepage wall is more than 50m. The seepage quantity reach 12 012m3 /d with the depth of anti-seepage wall is 50m.