Soil moisture is one of the restricting factors in a fragile karst ecological environment. However, its spatio-temporal evolution characteristics in the karst areas of China remain poorly understood. Thus, based on soil moisture from reanalysis (ERA-Interim product) and ground stations, this study used the Mann-Kendall test, the Theil-Sen slope estimator, sensitivity analysis and stepwise regression and obtained the following results: 1) ERA-Interim soil moisture well reflected the interannual change of observational soil moisture at 0-7, 7-28 and 28-100 cm. 2) The reanalysis and station data showed that soil at various depths in the karst areas was dominated by a drying trend in 1982-2015. 3) Soil moisture in karst areas of southern China was high but decreased fastest. In the karst areas of northern China, soil moisture was low and declined quickly. Nevertheless, soil wetting was observed in the central karst areas of Qinghai-Tibet Plateau. 4) Changes of soil moisture throughout the karst region of China and its subareas were mainly affected by precipitation, followed by temperature. 5) In Qinghai-Tibet Plateau and southern China, soil moisture in karst areas is overall higher than that in non-karst areas when under low vegetation coverage levels (NDVI <= 0.3) of some climate zones, possibly caused by the centralized allocation of precipitation in karst areas due to exposed rocks. In conclusion, climate, vegetation, and geological background make the spatiotemporal distributions of soil moisture differ within the karst region, while the soil drying trend in recent decades and global climate change are not conducive to the ecological restoration of vulnerable karst areas.