Abstract: The Analysis of climatic characteristics of temperature and humidity on the Xizang-Qinghai Plateau is made based on the data set from 123 stations on the Xizang-Qinghai Plateau and its vicinity. The results indicate that the region near 32°-33°N may be the divide of the climatic difference from south to north on the plateau. The northern plateau is influenced by dry and cold air and the southern by humid and warm air. Using the REOF method, we can separate the temperature and humidity on the plateau into different patterns and then analyze the characteristic of each pattern. The results indicate that in recent 40 years temperature has been increasing gradually, fluctuating with time. The temperature increase occurred mainly in the periods of 1978 to 1981 and 1983 to now, and the increase in the last period is the greatest. The amplitude of the temperature increase takes on a pattern of "big-small-big" from south to north on the plateau. The humidity in recent 40 years is also on the increase trend fluctuating with time in most part of the plateau, but the northern boundary of the plateau become drier. The main period of humidity increase is the late 1980s. The amplitude of humidity increase takes on a pattern "big-small" from south to north on the plateau; especially, the region around Qilian Mountain become drier.