As an important water conservation and sand-windy barrier, Zhangjiakou and Chengde (Zhang-Cheng) district is very important for ecological protection in the Beijing-Tianjin-Hebei region. The soil moisture is an important comprehensive indicator for climate, vegetation cover, and soil property, and is essential in the cycle of atmospheric−surface water−underground water. However, few studies focused on the soil moisture change and its impact factors in the Zhang-Cheng district, an area with semi-arid climate and scarce water resources. Based on moderate-resolution imaging spectroradiometer (MODIS) and global land data assimilation system data (GLDAS), the spatiotemporal variation of surface soil moisture in Zhang-Cheng district was simulated during the period of 2001−2021 using temperature vegetation dryness index (TVDI) model. Moreover, the geodetector method was also employed to identify the contribution of 8 impact factors on soil moisture. The results indicate that the soil moisture is generally fluctuating increase during the period of 2001−2021. Spatially, the soil moisture is higher in the east and lower in the west part of the study area and approximately 83.09% of the the study area experienced a progressive increase in soil moisture. In terms of driving factors, normalized difference vegetation index (NDVI), soil type, annual precipitation, land use type, slope, elevation, annual temperature, and aspect were analyzed in descending order of their effect on soil moisture variation. NDVI and soil type are the dominant drivers, with each contribution exceeding 30%. As to interaction analysis, it indicates that the effect of multiple factors is greater than that of individual factor. The synergistic interaction between NDVI and elevation is the largest influence on soil moisture. This study has great significance for efficient utilization of water resources and eco-environmental protection in the Zhang-Cheng district.