As an important ecological security barrier of north China,the Huangqihai Lake wetland is a farmingpastoral ecotone with extremely fragile ecological environment. The wetland suffers from the serious degradation caused mainly by the irrational exploitation of water and land resources as well as the drying of climate change during recent decades. In this paper,the main causes of wetland degradation were discussed,and it was considered that the lake drying-up was directly caused by the over-pumping of groundwater from the confined aquifers in the basin. The lake water balance model was developed to simulate the interaction of surface water and groundwater by using the numerical groundwater flow model. The inflows of the lake were calculated,and the results revealed that the water areas in normal,high-flow and low-flow years were 29. 83 km~2,31. 67 km~2 and 23. 79 km~2 respectively. The results of monthly water balance illustrated that the largest water area occurred in December instead of rain season, this was quite different from the previous hydrological results of the lake. The sustainable water areas of the lake for regenerating the ecology in the future were determined based on analyzing the hydrological regime,and they would be 20 km~2 and 30 km~2 in 2020 and 2030 respectively. The research results could be referred in planning the water resources exploitation and conserving the wetland in the basin.