Mining operations can usually lead to environmental deteriorations. Underground mining activities could cause an extensive decrease in groundwater level and thus a dramatic variation in soil moisture content (SMC). In this study, the spatial and temporal variations of SMC from 2001 to 2015 at two spatial scales (i.e., the Shendong coal mining area and the Daliuta Coal Mine) were analyzed using an improved thermal inertia model with a long-term series of Landsat TM/OLI (TM=Thematic Mapper and OLI=Operational Land Imager) data. Our results show that at large spatial scale (the Shendong coal mining area), underground mining activities had insignificant negative impacts on SMC and that at small spatial scale (the Daliuta Coal Mine), underground mining activities had significant negative impacts on SMC. Trend analysis of SMC demonstrated that areas with decreasing trend of SMC were mainly distributed in the mined area, indicating that underground mining is a primary cause for the drying trend in the mining region in this arid environment.