Abstract: In this paper, the monthly precipitation in Northwest China in summer is firstly resolved by EOF method. Then, the distribution characteristics of time and space of the resolved first main weight and eigenvector, and the correlation between the first main weight and OLR in the same time were analysed. Through comparative analysis, the result indicates that the difference between monthly dificient rainfull years and abundant rainfall years is obvious in summer in Northwest China, and that the precipitation in summer in Northwest China shows opposite tendency of that in Southern China.