Based on introduction,calibration and validation,the EPIC model was used to simulate water potential productivity (WPP) of winter wheat and soil water dynamics on rainfed highland at Changwu of the Loess Plateau for medium term (12 years) and long term (30 years) assessment simulation research respectively.The results show that:1)during the 12 year simulation period under real time weather conditions,WPP of winter wheat on rainfed highland fluctuates and decliness along with precipitation changes,crop available soil water amount in 3m soil layer also fluctuates and declines evidently,and trend of soil desiccation is remarkable;2)during 30 year simulation period under simulated weather conditions,WPP of winter wheat on rainfed highland fluctuates along with precipitation but declines slightly,crop available soil water amount in 3m soil layer fluctuates seasonally and annually,but without remarkable soil desiccation;and 3)after integrated analysis,it is thought that soil desiccation of wheat field on rainfed highland is a short time phenomenon and usually won't continue long if decline trend of precipitation is insignificant,but fluctuation of wheat yield along with precipitation change is inevitable.