Serious soil erosion in the purple hilly areas of Jialing River basin is the major source of soil and water loss in the lower and middle reaches of the river.Lizixi watershed in Sichuan Province was chosen as the study area.Land use data were extracted by RS and GIS technology from remote sensing images(Landsat TM/ETM+and Spot Images)in 1986

1999and 2001representing the conditions at the three periods before and after implementing the key control project of soil and water conservation in the upper reaches of the Yangtze River(referred to as the“Changzhi” project).The distributed hydrological model SWAT was used to simulate runoff and sediment yield based on the landuse data at the three periods.Based on the land use map in 1986

the impactsof land use changes and different climates on runoff and sediment yield inLizixi watershed were evaluated by making an assumption of 7different landuse conditions and 9different climate combinations.The simulated resultsshow that:(1)After the implementation of the“Changzhi” project

paddy fieldsand dry land area continued to decrease

and forest area continued to increase from 1986to 2001

which was mainly transformed from paddy fields and dryland.(2)The land use changes of increased forest area and decreased farmland had an obvious influence on runoff and sediment yield

which showed that the control measures

mainly in the form of returning farmland to forestry and afforestation

had effects on soil and water conservation.In terms of conserving water and intercepting sediment

forestry was better than grassland

and grassland was better than farmland.Taking the measure of returning farmland to forestry and grassland in>25°farmlands had more obvious effects on reducing surface runoff and intercepting sediment than 15°~25°farmlands.