Abstract:Seasonal division and trend characteristic of air temperature are made based on the daily temperature series at 486 stations for 41 years (1960~2000, totally 14976 days) in China. The method is the Hierarchical Cluster Analysis considering various criteria of inter-group and intra-group correlation coefficients. The following climate division and characteristics can be drawn out. The division number of sub-regions of summer (and summer months) is bigger than winter and other's seasons. The annual variation of temperature can be divided into 23 sub-regions. The numbers of sub-regions in winter and summer half year are 22 and the numbers in spring, summer, autumn and winter are 24, 28, 26, and 28. For twelve months from January to December the regional numbers are 24, 23, 18, 18, 18, 25, 19, 20, 29, 31, 18, and 24, respectively. Trends and variation characteristics of air temperature are different in various sub-regions and seasons. For the annual variation, the rising trend was noted in northern China while falling trend was found in the Sichun basin. A falling trend of air temperature was observed in the mid-low Yangtze River valley.