This paper introduced the method for evaluating carbon fixation and oxygen release service functions of urban forest ecosystem, and accounted the carbon fixation and oxygen release valuation of Changsha--the third National Forests Cities of China. The results showed that the carbon fixation and oxygen release valuation are about 2 712 millions RMB and 1 061 millions RMB per year, and the total valuation is about 3 773 millions RMB per yea...