Abstract: With the implementation of China’s Western Development Program，the excessive growth of population has become a bottleneck ahead for ecologically fragile areas. Meanwhile，with over-exploitation and utilization of water resources，the ecological and environmental problems have become more serious in river basin for the western regions. In particular，the environmental fragile zone is a sensitive monitor of water resource in arid and semi-arid regions. On the consideration of sustainable development strategies，a pattern for coordinated development of society，economy and environment is urgent to be proposed. It is，therefore，determination of stream’s ecosystem service value is of great importance in well understanding the status of river health and is great helpful for rational utilization of stream，ecosystem functions for social-economic development. As a case study，this paper focuses on the estimation of instream，ecosystem service value for the Weihe River in Shaanxi Province. According to related scientific theories and methodologies especially from the disciplines of ecology and economy as well as field investigation，the methods for estimation the stream’s ecosystem service value are proposed，which includes [C-D] production function method，market valuation method，shadow engineering method，opportunity cost method，recovery cost method，market price replacement cost method and so on. On the basis of calculation from these methods，the stream’s ecosystem service value for the Weihe River is determined. The results show that stream，ecosystem service value for the Weihe River of Shaanxi Province in a typical year of 2012 is 356.36 billion Yuan RMB，which accounts for 25% of total output value of the Shaanxi Province in the same year of 2012. Among the composition of stream’s ecosystem service function，the service values for provisioning，regulation，support and culture are 273.56，75.72，4.0 and 3.08 billion Yuan RMB，respectively. Obviously，the stream’s ecosystem service values mainly embody in provisioning service value and regulating service value. However，due to lack of measured approaches，the service values for research and education of the culture function are not estimated，which resulted in underestimation of provisioning service and regulating service values. Moreover，as each service function closely interact and influewcp the other service functions，this requires not only consideration of stream，provisioning service value，but also put more attention to the comprehensive values from other service functions. Otherwise，the whole stream，service value will be damaged. Furthermore，some effective protection measures should be put into effect when use stream water for social-economic development of the Weihe River basin．

Key words: The Weihe River, instream, ecosystem service function, value estimation