A long-term (9 years) field observation was carried out in the Plank Organic Farm in Nanjing to study dynamic changes in soil organic carbon and soil humus composition in vegetable soils different in cultivation mode (organic field, organic greenhouse and conventional field). Results show that the 9 years of vegetable cultivation increased soil organic carbon (SOC) from 11.41 to 15.35 g kg^-1, from 9.29 to 20.90 g kg^-1 and from 9.00 to 10.00 g kg-1, humic acid carbon(C_HA ) from 1.79 to 2.11 g kg^-1, from 1.23 to 3.11g kg^-1 and from 1.14 to 1.31 g kg^-1, and fulvic acid carbon(C_FA) from 2.19 to 2.44 g kg^-1, from 1.88 to 2.68 g kg^-1 and from 1.73 to 1.91 g kg^-1, in the organic field, organic greenhouse and conventional field, respectively. The increases in the soils under organic cultivation either in open field or in greenhouse were significant, but not so in the soil under conventional cultivation. C_HA / C_FAratio and PQ value are two important indicators characterizing quality of soil humus, and were both higher in the soils under organic cultivation than in the soil under conventional cultivation. E₄/E₆ratio and ΔlogK value of soil fulvic acid increased, too, in all the soils, but the increase grew more significant with age of the vegetable cultivation in the former than in the latter. Aromaticity of the soil humic acid displayed a trend of declining first and then rising, which was not so significant in the soil under conventional cultivation. All the findings indicate that long-term organic cultivation may not only be conducive to SOC accumulation, but also promote the process of soil humification.