Soil organic carbon and its labile components are sensitive indicators of changes in soil carbon pool. Therefore, the study on soil organic carbon and its labile components is of great significance to the research of global climate change. A field survey was carried out of tidal flats and natural wetlands in Hangzhou Bay with samples of soils at 0~10 cm, 10~20 cm, 20~30 cm in depth collected for analysis of changes in soil organic carbon (SOC), soil dissolved organic carbon (DOC), soil readily oxidizable carbon (ROC) and light fraction organic matter (LFOM) in bare mudflat and mudflats under Phragmites australis, Spartina alterniflora and Scirpus mariqueter, and relationships between various fractions of organic carbon and soil physico-chemical properties. Results indicate that (1) the mean SOC content in soils of the three soil layers was 3.87~5.08 g kg^-1, 6.46~6.78 g kg^-1, 4.33~4.48 g kg^-1 and 4.99~5.25 g kg^-1 in mudflat under Phragmites australis, Spartina alterniflora, and Scirpus mariqueter, and bare mudflat; the mudflat under Spartina alterniflora was the highest and followed by bare mudflat in mean SOC content; soil TN and SOC varied in a similar trend, regardless of vegetation; (2) The mudflat under Spartina alterniflora was the highest in mean DOC and LFOM content, being 90.69~98.90 mg kg^-1 and 2.35~2.95 g kg^-1 respectively, while the bare mudflat the lowest, however, the bare mudflat was the highest in mean ROC content, being 2.06~2.22 g kg^-1; (3) No significant difference was observed between the mudflats under Phragmites australis, Spartina alterniflora, andScirpus mariqueter in DOC/SOC ratio, but in ROC/SOC ratio, a decreasing order was found of bare mudflat > mudflat under Scirpus mariqueter > mudflat under Phragmites australis > mudflat under Spartina alterniflora; (4) SOC was significantly and positively related to DOC, ROC and LFOM; Besides, SOC was also significantly and positively related to TN and soil moisture content; but all the SOC fractions were negatively related to soil pH (p<0.01). All the findings indicate that the invasion of Spartina alterniflora is not so bad because the plants help enhance wetlands’ carbon sequestration capacity, and the labile fractions of organic carbon are good indicators of changes in soil organic carbon pool in wetlands.