Abstract: In the paper,some impo rtant nitrogen fixation trees and nitrogen fixingrates of some presentative specieses are introduced.In resolving some problems existing inthe construction o f Yangtze River conservation forest system,the roles that nitrogenfixation trees can play are identified as follows:1.increasing biodiversity in the Yangtzevalley,2; preventing soil erosion and infection of forest insect and disease,3.alleviatingthe confliction between forestry and agricuIture and increasing stability of ecology,4.re-ducing the riks of the program and encouraging participation of the local people.