The influence of rainfall in spring and summer on reservoir water capacity was analyzed on basis of analysis of the climatic conditions of two large reservoir′s control valley and the water storage character.The best correlation between the rain in the valley and the water level in late spring and late summer was put forward.When the rainfall in April and May reach 550mm and 400mm,the water level of Hongfenghu and Wujingdu in late spring and May will reach the normal high level respectively,and when the rainfall reach 780mm and 500mm in July and August,the water level in late summer also reach the normal level.