As a major natural disaster in China,drought is a restricting factor on the social and economic development. In the article, drought development process is simulated based on WHMLUCC model and Palmer drought severity index. A probability calculation method is proposed based on WHMLUCC model by the way of causes to inquire into the drought probability distribution on changing environment, and the drought event probability under different grade (such as non,light,medium,heavy and specially drought) is given,which could provide a scientific basis for drought forecasting and planning in the river basin. The results show that (1) the drought probability distribution shows a severe impact of climatic conditions on drought events, and LUCC has significant effects on drought on past climate condition, and LUCC has weak effects on present climate conditions;(2) comparing 5 scenarios,scenario 2 is beneficial to alleviate extreme drought, and the drought situation is relatively consistent on present climate condition, and (3) through cause analysis,it is known that the agricultural drought is closely related to climate change and the land use and land cover change in the Wuding River basin.