The fiver network is very dense in Dongting Lake area. In order to accurately evaluate the quantity of water resources, a water yield model was set up according to water quantity conservation theory and the concemed hydrologic and meteorological data. Underlying surface of the Dongting Lake area was divided into 4 layers, i.e. water surface, paddy field, water-impermeable layer and land. Different calculations were made for various layers. This model has been applied in yearly nature water yield calculation for 3 counties as calculation units in water body of Dongting Lake.