Abstract: A case study of the Heihui River,Panglong River and Longchuan River valleys was carried out to explore relationship between sediment discharge and land use in longitudinal river valleys in Yunnan.Results show that implementation of the "Grain for Green" policy,increased the area of forest lands and decreased the area of croplands and grasslands,thus,significantly reduced sediment discharge from the rivers.Whereas reclamation of forest lands into farmland or grassland or of grasslands into farmlands resulted in significant rise in sediment discharge.In the ten years following 1990,in the Hehui River and Panglong River basins the land use became more reasonable and as a result the annual sediment discharge appeared to be on the decline,while in the Longchuan River basin,the land use turned reversely,and so did the annual sediment discharge.The variation of sediment discharge in the three basins accorded with the general trend of the change in climate.Change in land use is the main cause of the variation of sediment discharge.Sediment discharge in the three river valleys follow the same general law for mountain rivers in responding to changes in land use.The response is much strong in mountainous areas than in flat areas.

Key words: longitudinal valley, land use, sediment discharge, response, Yunnan