Abstract:From three factors: valley's landforms, climatic changes and reservoir's effects, the cause is discussed that the Shengzhong reservoir in Sichuan province initially contains no enough water.Analytical result shows that there is no difference of the tendency distribution in space and time of the annual precipitation in the reservoir's location and nearby surrounding area. After its construction, the amount of precipitation around the reservoir is reduced that is less about 200mm than before. All the station's terrain around the reservoir is unchanged. After the reservoir storing water, the greatest impact is that the arnount of precipitation reduces nearly 40mm of points around it. There was a severe successive three-year drought after its construction. This suggests that the effect of climate on precipitation is much stronger than that of the reservoir. So climatic changes is the main cause that influences water amount of the reservoir during its initial use.