The purpose of the study was to constructa system dynamics model of soil and water loss on slope surface on the basis of system dynamics principles through the analyses of soil and water loss processes and its influencing factors. Experimentwas conducted on three runoff plots ( natural slope,forbidden slope,and level-terrace) in Yuanmou County,Yunnan Province located in the dry-hotvalley of Jinsha River. Data observed form the runoff plots were inputto model and the VENPLE software was used to find the processes of runoff and soil loss. Data of runoff and soil loss obtained from the simulation model were then compared with observed data. Relative error was found to be between 6. 9% and 17%. This illustrates thatthe system dy namics model is an ideal model.