Abstract:This study is aimed to investigate the dynamics of total soil organic carbon (TOC), light fraction organic carbon (LFC) and heavy fraction organic carbon (HFC) concentrations, their profile distributions and influencing factors in an anthropogenic-alluvial soil in the Minqin Oasis Area under six abandonment time series. In each sampling area soil samples were collected from 4 layers within 0–60 cm depth. The results showed that 1) TOC, LFC and HFC contents were between 3.21–5.23g/kg, 0.34–1.51 g/kg and 2.55–4.30 g/kg in this soil profile, respectively. TOC, LFC and HFC decline mainly occurred in the tillage layer (0–20cm) after 40 years abandonment, compared to conventional tillage, the annual decline rates of TOC, LFC and HFC were 1.94%, 5.46% and 2.13%, respectively. In general, TOC and HFC contents in 20–60 cm soil depth showed a slow increasing trend, compared with cropland under conventional tillage, the annual increase rate of TOC and HFC were 0.31% and 0.88%, but LFC continued to decline, with an annual decrease of 1.18%. 2) The HFC contribution to TOC was greater than LFC on abandoned land, soil TOC and HFC contents were significantly positively correlated with clay and silt percentages respectively, and significantly negatively correlated with the sand percentage, LFC content didn’t reach significant levels in statistics with silt, sand and clay percentages, but LFC content had significant or extremely significant relationship with pH, EC and SAR, indicating LFC was more sensitive to soil salinization. 3) Stepwise regression analysis showed that soil total nitrogen (TN) and TOC/TN ratio had greater impact on soil TOC, LFC and HFC. 4) With the long time abandonment, tillage layer became rough and salinity increased, which is not suitable for soil organic carbon accumulation; but with the soil horizon deepen, clay and silt percentages increased, which can increase soil organic carbon accumulation.