The paper used principal component analysis (PCA) to study the driving factors and overall trend of change of water resources carrying capacity according to ten years statistical data of GDP and total population in Yan'an city from 2001 to 2010.Based on the goals of economic and social development, it forecast the situation of supply and demand of water resources of Yan'an city in 2015 and 2020 by use of multiple linear regression model. The results show that the three components that affect carrying capacity of water resources are socioeconomic status, agricultural development level and water resource conditions. Moreover, population and GDP are the main driving factors., the carrying capacity water resources declined year by year In recent ten years. With the rapid development of social economy, the water shortage in Yan'an in 2015 and 2020 will be 38 million cubic meters and 46 million cubic meters respectively.The carrying capacity of water resources is serious short.