Qinghai-Xizang Plateau is sensitive to the Globe Change. It has been proved that, comparing to the average air-temperature of Northern Hemisphere, Qinghai-Xizang Plateau is becoming warmer faster. In this paper, 126 insitu air temperature observations over Qinghai-Xizang Plateau and anomaly temperature time-series of Northern Hemisphere are used to analyze the characters of air temperature variations over the Plateau. By using the correlation coefficient method, temperature distribution patterns and its variation are studied. The strongest periodic signal variations of abrupt change of air temperature are investigated by using the wavelet analysis and the M-K method. The results showed that the abrupt change of air temperature over the Qinghai-Xizang Plateau started from the border region of east and southeast Plateau and then occurred in north, northwest and west part. Abrupt change was not happened until late 1990s in south part of Tibet. This phenomenon had lasted for nearly 15 years since middle 1980s. At last, by analyzing and inter-comparing the air temperature abrupt change, the discrepancy between the actual observation and the result of the cycle analysis was discussed.