Wetlands exist in a transition zone between aquatic and terrestrial environments which can be altered by subtle changes in hydrology. Hydrological process determines the formation, development and succession of wetlands. Taking the Dongting Lake as a study area, this paper studies the hydrological recharge effect of the atmosphere precipitation. According to the meteorological data, remote sensing image and typical underlay feature data, the recharge effectivity of the rainfall on the Dongting Lake wetland is analyzed supported by GIS (geographical information system) technology and SCS (Soil Conservation Service) model. Based on the analysis of spatio-temporal feature of rainfall and modeling of the runoff of precipitation, we obtained ARC (area recharge coefficient) and VRC (volume recharge coefficient). Thus, ARC well explains the acreage relationship of watershed and that of the water area in the lake sometime. It presents not only the wetland hydrology feature depending on the recharge water, but also the recharge effect of the runoff coming from rainfall and its influence on the water area. However, it is difficult to illustrate water fluid in wetland resulting from precipitation recharge in a period. Considering the relationship between flux of rainfall-runoff and volume of lake, VRC is calculated to make up for the shortcoming of ARC. According to the model, the recharge effectivity of rainfall can be computed in a certain period. ARC, together with VRC, can better explain runoff coming from rainfall as well as how it affects Dongting Lake's hydrological process and how it recharges water to the wetland, including the water area and water cycle. Thus it is significant to realize the importance of rainfall to the wetland and to protect and manage Dongting Lake wetland.