The hilly area around Dongting Lake is a typical agro-forest multi-ecosystem in the hilly area of southern China.Rainfall resources are indispensable to water environment and water equilibrium in the ecosystem.Locational observations on water environment factors in the ecosystem and monitoring and research on water equilibrium in the small watershed were carried out.Results showed that the rainfall resources were rich in the region.But with the differences in seasonal allocation of rainfall,both surplus and deficiency occurs in the process of water balancing in the system.The seasonal surplus water was311.3mm,and the deficiency was134.7mm in the average year.About 76%of precipitation belonged to derivative resources for water cycle,and the remaining amount overflowed to downstream water area in the form of runoff.Some 1.31×10 10 m 3 of water,1.64×10 6 m 3 of silt and0.89×10 4 t of nutrients(N,P,K)in the area are lost or transported into Dongting Lake in the process of rainfall erosion each year.Thus rainwater conservancy is the basic form of the rainwater management .The utilizable rainwater is2.41times as much as the maximum requirement of irrigation water for the existing farmland at present,and the ratio of utilizable rainwater to requirement is related to ecosystem scale.The main factors affecting water equilibrium and water use efficiency are limitations of rainfall conservancy project and the construction of sloping land ecosystems,especially the construction of agro-forest multi-ecosystem.It contains the planting patterns of vegetation community and sustainable conservation of soil productivity.