Abstract:The variation trend，abrupt changes and anomalous years of annual and seasonal mean soil temperature at shallow layers from 1961 to 2005 in Xishuangbanna, Yunnan Province are investigated by using the statistical diagnostic methods such as linear trend analysis，accumulated variance and signalnoise ratio. The results indicate：(1) In terms of linear trend，the seasonal mean soil temperature in the shallow layers displayed a significant increasing trend in Xishuangbanna in past 45 years with an increase rate of 0.14 to 0.40 ℃/10a, maximum in winter，minimum in spring. The interdecadal variations of the annual and seasonal mean soil temperature in the shallow layers had an obvious increasing tendency, especially in winter and spring. (2) The abrupt changes of mean soil temperature in various layers occurred in autumn of 1980，and the abrupt changes in winter appeared in 1978; the period before the abrupt change is colder and the period after is warmer. Before the abrupt change, only annual mean soil temperature at 20 cm kept the same increasing trend, but a significant increasing trend after the abrupt changes, which shows that the annual mean soil temperature at 20 cm response to climate warming more sensitively since the 1980s. (3) Except that the annual mean soil temperature at 10 cm was anomalously lower in 1971，anomalously higher temperature occurred in 2003 at the other shallow levels. The results proved that the significant increase of air temperature is the main cause of the increase of soil temperature.
