Abstract: Spartina alterniflora has rapidly expanded from nothing at the salt marsh of Xichang Town, Hepu County, Beihai, Guangxi Zhuang Autonomous Region since 2011, which changed the landscape of the salt marsh wetland and may affect the carbon budget of the salt marsh wetland further. Based on satellite remote sensing images, the invasion year of Spartina alterniflora was determined. Then the relationship between the spatial distribution of soil organic carbon and the growth year of Spartina alterniflora in 7 sections of salt marsh wetland along Beibu Gulf of Guangxi in October 2019 were analyzed. Results showed that: (1) the spatial distribution pattern of soil organic carbon (SOC) in Spartina alterniflora salt marsh shaped like “M” along the coast; (2) the content of soil organic carbon increased with the growth of Spartina alterniflora in this salt marsh wetland and reached the maximum after about 5 years of growth; (3) the content of soil organic carbon (SOC) in Spartina alterniflora salt marsh increased with the coverage of Spartina alterniflora; (4) the average ratio of C/N in the Spartina alterniflora salt marsh was 12.5 (>12), indicating that the soil organic carbon was greatly affected by the terrestrial input.