[Objective] This study explored the characteristics of soil temperature changes in farmlands of Mollisol region in Northeast China in order to provide basic data for quantifying the degree of freeze-thaw action and its impacts on soil erosion.[Methods] Based on the data of soil temperature in 2 m soil profile and air temperature from November to next April in 2015-2018 at the typical farmland in Binzhou River basin of Heilongjiang Province, we analyzed the characteristics of soil temperature variation and its responses to air temperature changes during freeze-thaw processes and freeze-thaw times in plough layer in farmlands.[Results] The soil temperature increased with the increase of soil depth from November to next February, while declined with the increase of soil depth when the soil was completely melted. The maximum frozen depth was 80 cm in farmlands of the research region. Meanwhile, there was a significant positive correlation between soil temperature in 0-60 cm depth and air temperature, and this correlation decreased with the increase of soil depth. In contrast, soil temperature under 80 cm depth was negatively correlated with air temperature.[Conclusion] There was a unidirectional freezing and bidirectional thawing in the study area. The freeze-thaw action mainly occurred at 0-20 cm in the topsoil layer of farmland, both maxinum freeze-thaw cycle times were 12 and 7, respectively, which provided the scientific basis for the design of simulated Mollisol freeze-thaw cycle experiments.