Erdos Larus Relictus Nature Reserve is a typical inland wetland formed by a lake of semi-arid area, which was listed in the wetlands of international importance in 2002. Its rapid shrinking in recent years makes Larus relictus, the First-class National protected animal, almost disappear in this region. To explore the reasons for the lack of water in this wetland and more importantly to find the solutions to it, this paper performs a simulation of the eco-hydrological processes in the catchment based on the SWAT model. The simulation combined with an analysis of climate evolution indicates that as much as 10.043 million m3 is lacked in this wetland. Among the factors which cause the lacked water, climate factor resulted in 5.944 million m3 , forage consumed 3777 thousand m3, vegetation construction reduced a runoff of 240 thousand m3, and square-built wells and JieFuliu projects consumed as much as 92thousand m3. Meanwhile，the ecological water demand of the wetland is calculated. To better utilize resources in the region, the author puts forward some measures of controlling eco-hydrological processes to achieve the coordinated development of slope ecology, wetland and economy in the catchment, i.e., controlling the suitable scale of forage to be no more than 692 hm2, grazing appropriately to reduce the impact of vegetation construction, saving water, and laying out water conservancy projects reasonably.