The high- density buildings in urban areas actually occupy the underground space resource at a certain depth below them. The occupancy depth has a significant impact on the interconnected development of urban underground space (UUS). Therefore, it is imperative to ascertain the occupancy depth and spatial distribution prior to UUS planning. The occupancy depth of UUS corresponds to the depth of the foundational load- bearing stratum, and is contingent upon factors such as building height and the geological characteristics of the site. In this paper, a rapid assessment methodology for determining the occupancy depth of UUS based on building height and stratum thickness was proposed and applied to the study area of Hangzhou main urban area. Firstly, the mathematical assessment model was formulated employing building height data from surveys and collected foundation data. Subsequently, the rapid assessment of occupancy depth of UUS in Hangzhou main urban area was achieved by the GIS- based spatial analysis using the building data sourced from Baidu and the stratum thickness data generated by Hangzhou’s 3D geological model. The research results can provide an effective method of assessing the large- scale UUS occupancy requisite for UUS planning endeavors.