Abstract:Based on topsoil temperature and snow data from 2009 to 2019 in the cold temperature needle-leaved forest in the Huzhong National Nature Reserve of the northern Daxing'anling in Northeast China, this paper analyzed the characteristics of topsoil freeze-thaw processes in the permafrost regions in recent ten years, including frequency and days of freeze-thaw cycle, start and end time, duration, fluctuation, etc. The thawing stage of topsoil mainly occurred from mid-late April to mid-May and the freezing stage started from mid-late September to mid-October. The average freeze-thaw cycles were 39 times or 41 days per year. There was no significant difference in the average frequencies or days of freeze-thaw cycles between the thawing and freezing stages. However, the fluctuations of topsoil temperature in freezing stage (mainly between 2.6 °C and 15.0 °C) were higher than those in thawing stage (mainly between 2.6 °C and 12.5 °C). The start date of the thawing stage was basically consistent with the disappearance time of snow cover, but the appearance time of snow cover almost occurred after the end of the freezing stage. Therefore, the topsoil was seldom covered by snow in the thawing and freezing stages, and the freeze-thaw cycle was mainly affected by the variation of air temperature. This study provides scientific bases and references for understanding the responses of permafrost to climate change and formulating the appropriate strategies in Daxing'anling in Northeast China.