Abstract: The objective of this study was to explain changes in the spatial distribution and dynamics of soil organic carbon (SOC) in grasslands converted from farmland in the Lanlingxi watershed, Yichang City, and thus to provide a theoretical basis for assessments of the carbon sink function of abandoned farmland. The experimental scenario subsets included a control group (A₁) and a split-plot design with C₄ plant (Rhizoma cyperi) litter removal (B₀) versus double litter input (B₂) in 2008. Soil samples at different depths were collected at the end of March from 2008 to 2015. SOC density was determined and the results are as follows. 1) After the return of farmland to grassland, the balance of SOC density was disrupted and carbon sink functions initiated. The time taken for SOC density to reach a new dynamic equilibrium was 12 years. The annual rate of SOC sequestration was 263.5 g/m². 2) In 2008, SOC densities in the three experimental areas ranked in the order: B₂ (5504±245 g/m²)>B₀ (5476±267 g/m²)>A₁ (5392±306 g/m²); but by 2015 the rank order had changed to A₁ (6022±298 g/m²)>B₀ (5963±315 g/m²)>B₂ (5807±274 g/m²). Not only plant species but also the amount of litter can affect variations in organic carbon density. 3) SOC densities in the control (A₁) and litter removal (B₀) areas increased continuously during the study period, while the double litter area (B₂) fluctuated in 2009-2011 and then increased continuously. Control area (A₁) conditions were more conducive to the accumulation of SOC. 4) The changes in SOC affected by plant species and the amount of litter were mainly at the 0-20 cm soil layer, while at layers greater than 20 cm there was no change. SOC densities at different depths of farmland and grassland soils were significantly different (P<0.05). The spatial distribution of SOC density in all three experimental areas changed during the farmland-grassland succession process. The amounts of SOC accumulation varied significantly during the transition from farmland to grassland.