Based on the seasonal distribution character and its change about cloud and water vapor in Qilian mountain, the results as following: The total cloud is most in spring and it is take second place in summer. The low cloud is most in summer, it is take second place in spring. Both total cloud and low cloud is least in autumn and in winter. During the past 45 years, total cloud is decreasing and low cloud is increasing in spring and in summer, the precipitation is increasing at the same time, total cloud and low cloud and precipitation have a decreased tendency in autumn, total cloud and precipitation is adding in winter, but low cloud is reducing in winter. There are positive correlation between total cloud and precipitation in summer and in autumn. The positive correlation happened between low cloud and precipitation in spring and in summer and in autumn, but has negative correlation in winter at the middle and eastern part of Qilian mountain, which is not notable in winter. Vapor flux is transported to the Qilian mountain areas along two path, there is strong vapor flux convergence in this region, the value is from 0.1 to 0.05 kg/(m2·s) in the eastern part of Qilian mountain and is from 0.05 to 0 kg/(m2·s） in the middle and western part. Med and the Caspian sea and the Black sea and the Aral sea are the headstream of water vapor of Qilian mountain, but it is different in every season. The net vapor flux value is positive in spring after 1979 and which is adding also, which is positive and has a increasing trend in summer in past 45 years, but is negative in autumn and in winter. In brief, the water vapor resource in Qilian mountain has a good potency for exploitation in spring and summer.