Hongxing reservoir was constructed on the floodp lain of Hulan River in Heilongjiang. The geological problem of the reservoir is the seepage of the dam base and its related seepage stability. The leakage of the reservoir is caused by the water head differences between the up stream and downstream of the dam. Severe seepage could decrease the engineering benefits of the reservoir. Moreover, infiltration function of water will influence the safety of the dam. Through the analysis on the granule constitute and the formation of the dam base, the types of the seepage failure apt to happen were defined and the anti-infiltration and the permissible dep ression ratio were determined. Using the numerical simulation software GMS, the two-dimension numerical modeling has been carried out to analyze the seepage field of the reservoir. Through the two conditionsmodelingwith concrete impervious wall and no concrete imperviouswall, the largest flow rate, single-wide seepage discharge and the max infiltration gradient of the dam base were calculated. According to the permeable dep ression ratio of the dam base, the seepage stability of Hongxing reservoir dam base was analyzed.