Accurately accessing spatial variability of farmland SOC and its main driving factors at provincial scale has great influence in regulating soil carbon and environmental protection. The spatial variability of farmland SOC of Jiangxi Province and its controlling factors were quantitatively studied based on 16 582 farmland topsoil samples(0-20 cm) collected in 2012 with the methods of ordinary kriging, variance analysis and regression analysis. The results showed that farmland SOC ranged from 5.22 to 40.31 g/kg, with an average of 17.90 g/kg and the coefficient of variation of 31.01%. The range of farmland SOC was 30.6 km, the nuggest/still ratio were 12.49%, indicating the structural factors played a more important role in the spatial variability of SOC than stochastic factors.The high value of SOC are mainly distributed in Pingxiang, Xinyu, Nanchang, Fuzhou and Jingdezhen.Terrain factors, irrigation capacity, parent material, farmland-use type, soil type and straw returning patterns had significant impact on the spatial variability of SOC(P<0.01), but the influence degrees were different, in which straw returning pattern could explain 38.9% of SOC spatial variability and could be regarded as the main controlling factor of spatial variability of farmland SOC in Jiangxi Province.