Profile soil moisture (PSM), which is essential for a comprehensive understanding of the entire soil layer water content, is more difficult to retrieve than surface soil moisture (SSM). It is an effective approach to estimate PSM at regional scale by combining multi-source data. Based on random forest regression (RFR), this study established SSM-deep layer soil moisture (DLSM) relationship models for different seasons with in-situ observations over China. European Space Agency Climate Change Initiative Soil Moisture (ESA CCI SM) product was used to estimate DLSM. Spatiotemporal variation of SM in 10 soil layers, i.e., 0-10, 0-20, 0-30, 0-40, 0-50, 0-60, 0-70, 0-80, 0-90 and 0-100 cm, in China from 1980 to 2019 was analyzed in detail. ESA CCI SM product matched well with in-situ observations, but the former was generally higher than the latter. A method using saturated soil water content and wilting point for range constraining was proposed, which effectively reduced the overestimation error of ESA CCI SM product. As a whole, accuracy of RFR models was the highest in autumn, followed by summer and spring, and the lowest in winter. The models performed best in arid zone (ARZ), followed by temperate zone (TEZ) and cold zone (COZ), and worst in Qinghai-Tibet zone (QTZ). The multi-year mean and standard deviation of soil water storage of 10 soil layers were 1.64±0.11, 3.50±0.21, 5.29±0.30, 7.13±0.38, 10.04±0.46, 12.25±0.54, 14.47±0.62, 16.75±0.69, 19.05±0.76, and 21.36±0.83 cm, respectively. Soil profile was divided into fluctuating layer (0-40 cm), leap layer (40-60 cm) and stable layer (60-100 cm). Water storage of 1-m soil layer (WS-1m) over China increased from northwest to northeast and southeast, with lower PSM and greater heterogeneity in cold and arid regions and higher PSM and lower heterogeneity in warm and humid regions. WS-1m in tropical zone (TRZ), ARZ and QTZ peaked in summer, while that in TEZ and COZ was the lowest in summer. Soil profile became wetter in wet zone and wet season and drier in dry zone and dry season over the last 40 years. WS-1m in TRZ significantly increased after 2004-2009, and that in ARZ increased and decreased during 1985-1986 and 2013-2014, respectively. The main cycles of WS-1m over China were 5 a and 11 a.