Using the summer total cloud cover of 34 observational stations in June,July and August in the period of 1961—2000 in the Qilian mountainous region,the spatial anomaly features and time evolution rule of summer total amount over the 40 years were analyzed with EOF,REOF and spectral analysis method.The results show that the accumulative variance contribution of the first three EOF principal components accounted for 78% of the total variance,and the three principal components well reflected the global anomalous structure of the summer total cover,i.e.consistent principal part type,southeast-northwest opposite variation type,northeast-southwest opposite variation type,respectively.The accumutative variance of the first three REOF principal components accounted for about 74% of the total variance,and the first three loading vector fields represented the three major anomaly-sensitive areas well:the Qilian plateau region,the southeast of the Qilian mountain,and the east of the Hexi corridor,respectively,and their representative stations are Gaur ditch,Yongdeng and Minqin.The temporal evolution of the total cloud cover at the three representative stations showed different trends,but with the same 20-year and 10-year periods.