In this study, the daily remote sensing data of surface soil moisture with 1 km spatial resolution in the Yangtze River Delta region from April 2015 to December 2018 were analyzed, the temporal stability of soil moisture was assessed by the mean relative difference (MRD) and its standard deviation (SDRD) for each pixel of the data, and random forest model was employed to explore the impact of environmental factors like topography, climate, and human activities on the temporal differentiation and stability soil moisture. The results showed that: 1) In terms of interannual variation, MRD of soil moisture in study area exhibited a gradual decrease in spatial variation from north to south, while SDRD showed the opposite trend. 2) In terms of seasonal change within a year, the spatial variation of soil moisture MRD was more significant. The fluctuation was more pronounced in spring and winter compared to summer and fall. And the spatial variation of SDRD was less distinct, and the distribution of middle- and high-value zones differed. 3) The spatial distribution of soil moisture MRD was closely correlated with elevation, slope and precipitation. As MRD increased, these factors also showed a tendency to increase. However, the distribution of SDRD exhibited an opposite trend, while other environmental factors affected its spatial distribution. 4) Climate and topography factors exhibited the highest contribution to time stability of soil moisture in study area, and other environmental factors had varying degrees of influence depending on the season and soil cover type.