Under a long-term experiment on different fertilization treatments, the contents of water-soluble organic carbon (WSOC) in the soil ranged from 32.1 to 45.5 mg kg^-1, following the order of NPK+4500 kg rice straw>NPK+2250 kg rice straw>CK>NPK. The percentages of WSOC to total soil organic carbon (TOC) ranged from 0.15% to 0.19%, following the order of NPK+4500 kg rice straw≈CK>NPK+2250 kg rice straw>NPK. The contents of WSOC had significantly positive correlations with both TOC and soil microbial biomass carbon(SMBC). ¹³C-NMR results showed that WSOC were mainly com posed of carbohydrates carbon, carboxyl carbon and long-chain aliphatic carbon. Under different fertilization treatments, the coefficients of variation (CV) of WSOC/TOC and SMBC/TOC were lower than those of their absolute contents in soil. Furthermore, the CV of WSOC/TOC was higher than that of SMBC/TOC. The percentage of WSOC to TOC was a good indicator of the quality of soil organic matter under different fertilization treatments.