Existence of impervious surface areas (ISA) in cities strongly influences the physical and chemical characteristics of regional soil, therefore, has profound impact on ecosystem carbon cycle at multiple scales. However, due to the inaccessibility of soil sample beneath urban ISA, we know little about the biochemical properties and distribution pattern as well as the importance of soil organic carbon under urban ISA (SOCISA). To clarify this issue, 100-cm-depth soil profiles from 27 paired ISA and pervious surface areas (PSA) sites in northern Tianshan urban cluster in a dryland environment of northwestern China were taken. In order to estimate total soil carbon storage, urban land cover was retrieved from cloud-free Landsat8 images. Based on the data of land cover area and SOC, the soil carbon storage of this urban cluster was calculated. (1) averaged 100-cm-depth SOCISA of the northern Tianshan urban cluster is 5.74±0.39 kgC·m-2, which is significantly lower than the paired soil organic carbon of PSA (SOCPSA) of 8.69±0.75 kgC·m-2, about 52% of the latter (p<0.01); averaged soil bulk density (BD) under ISA BDISA=1.58±0.02 g·cm-3, which is significantly higher than its paired BD of PSA of 1.51±0.02 g·cm-3, about 5% of the latter (p<0.01). (2) SOC and BD of both ISA and PSA declines with depth. The results of linear fitting between SOC, BD, and depth show that SOCISA and BDISA have significantly declining trends, however, SOCPSA and BDPSA does not show such clear trend. In addition, SOCPSA at the 60~100 cm soil layers is significantly higher than SOCISA but there is no stable correlation between them. (3) Carbon storage hidden under ISA of northern Tianshan urban cluster is 68% of the total urban carbon storage and for individual cities this percentage is higher than 50%, therefore, SOCISA is the main part of the urban SOC storage. By revealing the SOCISA and its distribution, this study can facilitate the understanding of biochemical characteristics of soils beneath urban ISA, which is significance for estimating carbon cycling in both urban and global ecosystems.