Abstract: Based on the soil species data from the Second National Soil Survey, the soil organic C (SOC) density and stocks in East China were calculated, and the influnce factors of SOC turnover in cultivated soils were investigated by field and laboratory experiments.The results show that the SOC densities to the profile depth in Northeast China varied from 2.5 to 73.3 kg C/m² with a mean value of 10.5 kg C/m².In southeast tropical and subtropical China, the mean SOC densities to the profile depth ranged from 3.9-16.7 kg C/m² with a mean value of 9.52 kg C/m².With the increase of lignin content in plant materails and soil clay content, the decompostion rate of plant materails decreased in the cultivated soils.However, the increase of soil temperature, pH and CaCO₃ content promoted the decompostion of plant materails.For the same soil, plant materails decomposed faster in upland soils then in waterlogged paddy soils.The effect of climate conditions on the decomposition of plant materials could be sheltered by the comprehensive influnce of the compositon of plant materials and soil pH, and the effect of soil texiture disappeared with the occurrenceof soil free CaCO₃.