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Using the meteorological observation records of frozen soil from eight stations during the period of 1962 to 2008 in Datong, by means of linear trend estimation and accumulated anomaly methods, an analysis is made of the variation characteristics and influencing factors of frozen soil, such as the dates of beginning to freeze and completely defrosting, freezing duration, and the maximum depth of frozen soil. The results show that the largest permafrost depth reduced; the date of freezing beginning delayed; the date of defrosting advanced, the freezing duration shortened in general. Frozen soil is not only affected by the temperature, and local factors have great influence on the maximum depth of frozen soil.