Abstract: An analysis on variation trends and annual variation characteristics of monthly average air temperature,average maximal air temperature,average minimal air temperature,average air temperature at 2 A.M.and average air temperature at 2 P.M.during 1981-2005 in Wulanaodu Region was carried out.The results showed that the five lists presented a discontinuous increased trend of temperature in past 25 years.The linear increasing rate of maximal air temperature(0.78℃/10a) is maximal,and is 5.6-fold of that of minimal air temperature(0.14℃/10a).The average maximal air temperature and minimal air temperature presented an increased trend in all seasons.The increasing trend of air temperature in spring was most obvious,and the trend in autumn,summer and winter were gradually reduced. The increased range of air temperature,presenting obvious unsymmetrical variation,was higher in daytime than that at night.

Key words: Horqin Steppe, Horqin Steppe, Maximal air temperature, Minimal air temperature, Unsymmetrical variation