<p>Disentangling the driving mechanisms of urban impervious surface (UIS) spatial changes is critical for developing effective urban growth planning. However, previous studies often overlooked the indirect effects of multiple factors especially inter-urban spatial interaction and policy factors on urban expansion in urban clusters. Here, we used structural equation modeling and geographically weighted regression to quantify the spatiotemporal patterns of direct and indirect effects of socioeconomic factors, geographical environment, inter-urban spatial interaction, and policy factors on urban expansion in the Beijing-Tianjin-Hebei (BTH) region from 1990 to 2020. The findings showed that urban population, inter-urban spatial interaction, tertiary industry, road density, and policies were the main drivers of UIS changes. Among them, inter-urban spatial interaction primarily had an indirect positive effect on urban spatial patterns by increasing urban population and optimizing industrial structures, with the strongest impact in southern BTH. Regional planning policies such as development zones promoted urban expansion by stimulating industrial development and attracting urban population, with their influence escalating from 0.41 in 1990 to 0.57 in 2010. These findings highlight the importance of strategically guiding inter-urban spatial interactions and optimizing industrial layouts to foster compact urban development and sustainable land use in the BTH region.</p>