The semi-arid agro-pastoral ecotone is a transitional zone from agriculture to animal husbandry, with a fragile ecological environment. Top soil moisture (TSM) is an important factor restricting regional development, and studying its spatiotemporal changes and driving factors are important for ecosystem restoration. In this study, the spatiotemporal changes of TSM from 2003 to 2022 were analyzed based on empirical orthogonal function (EOF) method, and the individual and interactive effects of the influencing factors on the temporal or spatial variation of TSM were explored based on geographical detector model (GDM) method. The results showed that climate factors were the main influencing factors on the global spatial variation of TSM, while topography and soil texture had an impact on the local spatial variation of TSM. The explanatory power of the interaction among influencing factors on TSM was greater than that of individual factors on TSM, especially the combination of climate factors, where the combination of temperature, Pet and SPEI was the strongest explanatory power under each vegetation type. Precipitation and NDVI were the main factors affecting the temporal variation of TSM. This study provides insights into the spatiotemporal variations in TSM and its influencing factors in the semi-arid agro-pastoral ecotone.