Abstract: 【Objectives】 Evolution characteristics of soil particulate organic carbon and their relationship with soil fertility were studied based on a long-term paddy field experiment. 【Methods】 Based on a long-term paddy field experiment with different winter green manures located at Qiyang Red Soil Experiment Station, Chinese Academy of Agricultural Sciences, soil particulate, particulate organic carbon and soil nutrient contents of historical soil samples from 1982 to 2012 with 6 years?? interval were analyzed. There were four treatments in this study, rice-rice-winter fallow, rice-rice-rape, rice-rice-milk vetch and rice-rice-ryegrass. Soil samples in 0-20 cm layer were collected after the harvest of late rice, and soil particle size fractionation with the Anderson centrifugal was conducted to get sand (53-2000 m), coarse silt (5-53 m), fine silt (2-5 m), coarse clay (0.2-2 m) and fine clay (0.2 m). The contents of organic matter were determined by the potassium chromate method. 【Results】 1) After the 30 years?? application of green manures, the contents of soil organic carbon in different soil particulates had the trends as: fine clay (28.05-28.27 g/kg) coarse clay (25.76-26.91g/kg) fine silt (12.8-14.52 g/kg), sand (13.83-14.92 g/kg) coarse silt (1.67-2.62 g/kg). Compared with the winter fallow, the total organic carbon in soil, the organic carbon contents in fine clay and coarse clay were increased significantly by 34.6%-42.4%, 12.3%-13.2% and 6.1%-10.9%, respectively, while the organic matter contents in sand were decreased significantly by 26.2%-31.6% (P0.05). 2) The distribution proportion of soil organic carbon in different soil particulates after 30 years?? green manure planting were: coarse sand (45.0%) fine silt (25.8%) fine clay (15.1%) sand (11.5%) coarse silt (2.7%). Compared with the winter fallow, the proportions of organic matter were increased by 8.0%-12.8% in coarse clay, decreased by 36.8%-42.9% in sand, and elevated by 5.3%-6.1%, 5.5%-6.4% and 6.5%-8.1% in fine clay, fine silt and coarse silt, respectively. 3) The significant positive linear correlations were found between the contents of total soil organic carbon, the organic carbon in coarse clay and fine clay and cultivation years (P0.01) in the treatments with green manures. The accumulation rates of the total organic carbon, the organic carbon in coarse clay and fine clay were 0.16 g/(kga), 0.31 g/(kga) and 0.22 g/(kga) respectively; the contents of organic carbon in sand, coarse silt and fine silt had negative correlations with cultivation years (P0.05), the reduction rates were 0.59 g/(kga), 0.35 g/(kga) and 0.19 g/(kga), respectively. The average annual accumulation rate of organic carbon in coarse clay was 1.5%, which was 1.5 times of that in fine clay; the average annual accumulation rate of organic carbon in coarse silt was 2.7%, which was 2.8 and 1.5 times of those in fine silt and sand, respectively. 4) The organic carbon contents in fine clay and coarse clay had significant positive linear correlations with the total soil organic carbon (P0.01), while the organic carbon in coarse clay had the closest relationship with total soil organic carbon. The significant linear correlations were also found between the contents of organic matter in fine clay, coarse clay and some of the soil nutrition indexes, including soil total nitrogen, total phosphorus, available phosphorus, available nitrogen and available potassium (P0.01), while the organic carbon in coarse clay had the closest relationship with soil nutrition. 【Conclusions】 The content of organic carbon in coarse clay was higher than those in other soil particulates, it was the most important component of organic carbon in the paddy soil; the organic carbon in coarse clay had stronger carbon fixation ability and most sensitive response to the change of total soil organic carbon, it was the most stable part of organic carbon in paddy soil. The organic carbon in coarse clay had the most significant correlations with soil nutrition, which was closest to soil fertility. The organic carbon in coarse clay could be an important indicator for soil fertility.