［Objective］This study aimed to analyze the temporal and spatial variation characteristics of soil moisture on the northern slope of the Tianshan Mountains and its influencing factors，with a focus on examining the impact of cropland expansion on soil moisture. ［Methods］ Based on 1 km daily soil moisture data， land use data， meteorological data，and other datasets from 2000 to 2020，the Theil-Sen Median trend analysis，Mann-Kendall significance test，and Pearson correlation analysis were employed to investigate changes in soil moisture within the 0-50 cm soil layer. Additionally，the Geodetector model was used to identify the main factors influencing soil moisture and their spatial differentiation characteristics.［Results］From 2000 to 2020，soil moisture in the 0-50 cm layer on the northern slope of the Tianshan Mountains exhibited an overall decreasing trend，with the most significant changes observed in the 0-10 cm layer. Under different land use types，soil moisture in croplands decreased significantly，while changes in forestlands and unused lands were not significant，and grasslands showed a slight increase in soil moisture. The average soil moisture followed the order of forestlands>grasslands>croplands> unused lands. Spatially，soil moisture decreased in most areas，but increased in the northern，southern，and eastern regions of the studied area. Soil moisture generally showed a downward trend across different elevation ranges，but gradually increased with rising elevation. When unused lands were converted to croplands，soil moisture increased at all depth levels，particularly at the 0-10 cm depth. The reduction in soil moisture was relatively small when grasslands were converted to croplands，whereas the decrease was more pronounced across all depth levels when forestlands were converted to croplands，particularly at the 40-50 cm depth. Vegetation type，precipitation，and potential evapotranspiration had the greatest impact on soil moisture，with influence values of 0.63，0.57 and 0.51， respectively. Among these factors，the interaction between precipitation and vegetation type had the most significant effect on the spatial heterogeneity of soil moisture.［Conclusion］From 2000 to 2020，soil moisture on the northern slope of the Tianshan Mountains showed a declining trend，with over 80% of the area experiencing a decrease in soil moisture. Soil moisture decreased significantly in croplands，it also declined when forestlands and grasslands were converted to croplands. Soil moisture variation was primarily significantly influenced by the interaction between precipitation and vegetation type.