Spartina alterniflora was introduced into China in 1979, and the first plantation of S. alterniflora was successfully constructed in Jiangsu province in 1982. Since it expanded quickly on coastal wetlands, great attentions were paid to its positive and negative effects on native ecosystems. In order to study the components and structural characteristics of soil organic carbon (SOC) pool of S. alterniflora saltmarsh, field observations and soil sampling work were fulfilled at permanent study sites including mudflat (MF), S. alterniflora salt marsh of 1-year (SAF2011), 5-year (SAF2007), 12-year (SAF2000), 23-year (SAF1989) and Suaeda salsa saltmarsh (SSF1989) along the coastal wetland in Yancheng, where located the largest area of S. alterniflora saltmarsh in China. The topsoil SOC, dissolved organic carbon (DOC) and microbial biomass carbon (MBC) were analyzed, and nuclear magnetic resonance (NMR) spectroscopy was utilized to explore the structure of soil organic carbon. The results showed that: (1) the development of S. alterniflora promoted the soil organic carbon sedimentation. The range of SOC was between 0.82-7.60 g/kg, which occurred as the order of S. alterniflora saltmarsh (5.57 g/kg) > S. salsa saltmarsh (2.4 g/kg) > mudflat (1.05 g/kg); the DOC occurred as the order of S. alterniflora saltmarsh(36.08 mg/kg) > S. salsa saltmarsh(17.43 mg/kg) > mudflat(6.92 mg/kg); the MBC occurred as the order of S. alterniflora saltmarsh(52.51 mg/kg) > S. salsa saltmarsh(18.27 mg/kg) > mudflat(13.56 mg/kg). These indicated that the soil active organic carbon pool was enhanced by the development of S. alterniflora. (2) The SOC contained more alcoxyl and aromatic carbon than other carbon fractions. The average proportion of SOC fractions occurred as the order of aromatic carbons(35.85%)> the alcoxyl carbon (32.83%) > carboxyl carbon (20.62%) > alkyl carbon (11.76%). The highest value of aromatic carbons, alcoxyl carbon and alkyl carbon occurred at the 5-year S. alterniflora saltmarsh(SAF2007), while the highest value of carboxyl carbon occurred at the 23-year S. alterniflora saltmarsh(SAF1989). (3) The ratio of alkyl carbon/alcoxyl carbon in topsoil occurred as the order of SAF2007 (0.44) > SSF1989 (0.43) > SAF2000 (0.28) > SAF2011(0.27) > SAF1989 (0.22); the ratio of hydrophobic carbon/hydrophilic carbon occurred as SAF2007 (0.97) > SSF1989 (0.87) > SAF2000 (0.85) > SAF2011 (0.83) > SAF1989 (0.81). The highest ratio of alkyl carbon/alcoxyl carbon (0.44) and hydrophobic carbon/hydrophilic carbon (0.97) occurred at the 5-year S. alterniflora saltmarsh(SAF2007), indicating the highest degree of alkylation and stability of SOC pool.