The content of soil organic carbon (SOC) and SOC density (0 ~ 40 cm) in the costal saline-alkali soils of Jiangsu Province under five vegetation types (Bare saline soil, BS; Artemisia wasteland, AW; Grass wasteland, GW; Rice-rape rotation, RR; and Continuous cropping of Jerusalem artichoke, CJ) were determined, and soil microbial biomass carbon (SMBC), dissolved organic carbon(DOC) and the ratio of SMBC, DOC to TOC in topsoil (0 - 20 cm) were also analyzed. The results showed that: (1) the content of organic carbon decreased with the increase of soil depth. SOC content and stock in the topsoil was 2.02 - 9.61 g/kg and 5.87 - 21.54 t/hm2, respectively. Topsoil SOC content and stock increased as the process of succession (BS→AW→GW) and significantly increased after three years farming in the GW soil, compared to GW, topsoil SOC stock of the RR and CJ increased by 55% (5.77 t/hm2) and by 107% (11.15 t/hm2), respectively. (2) The contents of SMBC and DOC in the topsoil were 21.7 - 449.1 mg/kg and 10.8 - 43.7 mg/kg respectively. SMBC was mainly in the depth of 0 ~ 10 cm. SMBC and SMBC/TOC were highest in CJ, the followed by GW, RR, AW and BS. The DOC and DOC/TOC decreased significantly after farming. Our results suggested that, the organic carbon pool and active organic carbon component successively increased with the wild vegetation succession, SOC stock in the costal saline-alkali soils increased after agricultural use for three years, while the ratio of the active organic carbon decreased. The main reason for the variation of the active soil organic carbon pool might be the land use change. Therefore, the increase of total SOC pool in China saline-alkali lands will be significantly important to reduce CO2 emission, however, it is worth mentioning that to take measures to improve the soil quality for ensuring sustainable productivity.