Land use has a profound impact on the accumulation and stability of soil organic carbon (SOC) by changing soil moisture conditions, carbon input pathways and microbial metabolic environment. However, there is still a lack of systematic understanding of the accumulation characteristics of microbial residual carbon (MNC) and the different mechanisms of its contribution to SOC under different land use types. In this study, the paired paddy soils and upland soils in four typical agricultural areas of Yujiang, Jishui, Xinfeng and Yifeng in Jiangxi Province were used as the research objects to determine the soil physicochemical properties, SOC content and microbial necromass carbon based on amino sugar index. The composition characteristics of soil carbon pool and its environmental driving factors under different land use types were systematically compared. The results showed that the SOC content of paddy soils was significantly higher than that of upland soils in the four regions, which was 1.5~3.0 times higher than that of upland soils. At the same time, the contents of MNC, fungal necromass carbon (FNC) and bacterial necromass carbon (BNC) in paddy soils were significantly higher than those in upland soils, indicating that long-term flooding environment and high organic carbon input promoted the accumulation of microbial necromass. However, the contribution of MNC to SOC in upland soils (21.55%~46.06%) was higher than that in paddy soils (23.36%~30.81%), indicating that microbial necromass carbon had a higher relative contribution to maintaining soil carbon pool under low carbon input environment. In different land use types, FNC content and its contribution to SOC were significantly higher than BNC, and fungal debris was the main component of microbial carbon accumulation in subtropical farmland soils. Random forest analysis showed that soil total nitrogen (TN) was the key environmental factor driving the accumulation of SOC, MNC, FNC and BNC.TN was significantly positively correlated with each carbon component, while NO3?, pH and available phosphorus (AP) were negatively correlated with it. In summary, land use patterns regulate the quantity and composition of farmland soil carbon pool by changing the status of soil carbon and nitrogen resources and the formation and preservation process of microbial necromass. Paddy soils had higher SOC and MNC accumulation capacity, while the relative contribution of microbial necromass carbon to SOC was higher in upland soils.