Large-scale vegetation restoration projects have been ongoing in the karst region of southwest China for several years. However, the influence of vegetation restoration alone on soil moisture (SM) changes in this region remains unclear. In this study, a random forest model was constructed using meteorological data, the ERA5-Land SM dataset, and the enhanced vegetation index to analyze SM changes in the karst region of southwest China caused by vegetation restoration alone. The results showed that on a monthly scale, vegetation restoration introduced an increase in SM that was mainly concentrated in January–April and a decrease that was mainly concentrated in June–August. On a seasonal scale, vegetation changes caused an increase in mean SM in spring and winter and a decrease in mean SM in summer and autumn. The largest increase in SM owing to vegetation changes was in spring, with an average increase of 0.019 m³/m³, and the largest decrease was in summer, with an average decrease of 0.010 m³/m³. However, the annual average SM increased only slightly. On the seasonal and annual scales, the coefficient of variation values for changes in SM caused by vegetation restoration alone were dominated by decreases, with a large decrease from January to April. In addition, vegetation restoration effectively moderated the drying tendency of soil caused by climate warming.