Distribution of organic carbon was studiedin soil profiles and organo-mineral complex,different in particle size,samp led from paddy fields varying in cultivation history,50,100,500,700,1 000 and 2 000 years in Cixi City, Zhejiang Province.Effect of long-term cultivation on structure and functional groups of humus in paddy soils was explored with the aid of infrared spectrum(IR).It seemed that cultivation history did not have much effect on organic carbon content in top soil of the paddy fields.Organic carbon content of the soil layers,30 to 60 cmin depth increased gradually with the cultivation history,but the range(Δ)of the variation of soil organic carbon reserves between two paddy soil layers,0～40 cm and 40～80 cmin depth respectively,decreased gradually.The findings show that paddy soils cultivated.