Abstract:River ecosystem service functions imply the natural environmental conditions and their effectiveness formed and sustained by river ecosystem and its ecological processes. River ecosystem service functions were divided into two groups by their types and effectiveness: river ecosystem products and river ecosystem services. River ecosystem products consist of the products and services harvested firsthand from river ecosystem, including water supply, fish resources, inland navigation, hydropower, recreation and cultural, and raw materials. River ecosystem services are functions to sustain the natural environmental conditions and ecological processes which are necessary for the human survival, including flooding control, soil and sand transfer, water resource storage, soil conservancy, environmental purification, nutrient cycling, and providing wildlife habitat. The accurate valuation of effects of dams on river ecosystem service functions is very important to environmental impact assessment of water conservancy projects and the maintain river ecosystem in China. On the basis of the effects features, an indicators system has been established to assess the effects of dams on river ecosystem service functions. Then, the effects of dams on river ecosystem service functions in China have been assessed and evaluated in the base year 2002. As a result, flooding control and hydropower generation were main functions of dams, and were up to 53.94% and 26.77% of positive effects on dams. Water supply, harmful gases release reduction, and inland navigation were also important functions of dams，and the value of each annually was 561.38×108 Yuan RMB, 141.25×108 Yuan RMB and 133.95×108 Yuan RMB. The total values annually of the dams positive effects on the river ecosystem service functions was 4410.98×108 Yuan RMB. The biggest negative effect of the dam was the reservoir sedimentation which lost annual values with -508.63×108 Yuan RMB. The second negative effect was reservoir inundation which lost annual values with -56.65×108 Yuan RMB. The occupation of the dam to the river ecosystem was also an important negative effects which lost annual values with -10.43×108 Yuan RMB. The total loss annually of the dams negative effects on the river ecosystem service functions was -575.71×108 Yuan RMB.