. The hydrological and erosional characteristics in the hilly area of Jialing River basin is strongly affected by a large number of water conservancy works such as ponds and reservoirs, which need to be considered in watershed runoff and sediment yield models when they are applied to this area. In this paper, a case study is presented which was carried out in the Weicheng River watershed, a representative small watershed in the Jialing River basin. A distributed model for small watershed runoff and sediment yield was developed based on analysis of pond and reservoir deposits. The impacts of land use changes from cropland to reforestation on runoff and sediment yield are simulated. The main results are as follows: (1) the physically based distributed model improves the accuracy of simulation results; (2) In the Jialing River hilly area, river channels and reservoirs are scoured during wet years, and the sediment will be deposited during dry years. During each year, the largest floods often flush down most of the sediment deposits, resulting to strong scouring of river channels while reducing the capacity of ponds or reservoirs. (3)Simulation results show that the annual runoff and sediment yield has been reduced because of reforestation. At the same time, evapo-transpiration, erosion, runoff and sediment yield during storm events were also reduced. The runoff decreased by about 0.7% and sediment yield by about 1.5%, when 10% of the area was reforested.