Based on data of mean air temperature during 1961—2005 from 8 meteorological stations in Alxa Plateau, the researchers analyzed the characteristics and variation trend of 4 sequences about the maximum and the minimum mean air temperature in summer and winter, and days of growth season and accumulated temperature in growth season. The change trend of the mean temperature showed a fluctuation and increase in recent 45 years, whereas the biggest increase extent occurred in winter for the maximum mean temperature, and the smallest increase extent occurred in summer for the minimum mean temperature. Temperature series showed a roughly linear increasing rate from southeast to northwest in Alxa Plateau, and the increasing rate in Bayanhot is equal to that in northwestern region of the Alxa Plateau. The hot days(≥30 ℃) increase obviously in recent years, and the variation of the warm days and the cool days is not obvious, while the cold days (≤-10 ℃) decrease obviously. The change of days of growth season is not obvious, but the accumulated temperature in growth season increases remarkably.