In order to understand the variations of soil moisture in response to rainfall events in humid karst area under shrub vegetation in winter, the response relationship was analyzed based on the daily monitored data of soil moisture and rainfall in this area. The results showed that 12 small rainfall events (less than 5.80 mm) could not replenish the soil moisture effectively, but the other two rainfall events (larger than 20 mm) could, and the response time of soil moisture increased with the increase of rainfall amount. According to the change trend of soil moisture, the change of soil moisture in winter was divided into three stages: soil moisture fading stage, soil moisture rising stage and soil moisture stable stage. In winter, due to the combined effects of vegetation interception and surface litter absorption, small rainfall events could not replenish the soil moisture effectively, the soil moisture was in a stable state or even decreased slightly; whereas heavy rainfall events could effectively replenish the soil moisture of the shrub, they promoted more water to penetrate into the deep layer of the soil, and significantly improved its moisture status. In addition, the lower the soil moisture before the heavy rainfall, the greater the rainfall replenishment to the surface soil moisture. In winter, the infiltration depth of shrub soil moisture was mainly affected by rainfalls with moderate intensity, long duration and heavy rainfall amount, and the higher the soil water content before the rainfall, the greater the infiltration depth of the rainfall.