Abstract: As C₄ plants, Spartina alterniflora has a strong carbon sequestration effect, and its biomass data can provide important parameters for assessing the carbon sink function of S. alterniflora. In this paper, by collecting and analyzing the research data on the aboveground and underground biomass of S. alterniflora in China, the temporal and spatial variation characteristics of S. alterniflora biomass in coastal wetlands of China and the relevant analysis results are obtained as follows: ① The aboveground biomass of S. alterniflora is higher from July to October, and the lowest in April and May; the underground biomass is higher from June to October, and the lowest from February to April, that is, the aboveground and underground biomass of S. alterniflora is higher in summer and autumn, and the lowest in spring. This seasonal variation pattern of S. alterniflora biomass may be determined by the life activity law of S. alterniflora itself. ② The biomass of S. alterniflora is different in different provinces, different regions of the same province and different habitats of the same region. The spatial differences of S. alterniflora biomass may be related to tidal action, latitude differences, rhizosphere soil microbial action, population invasion years and S. alterniflora species. ③The aboveground biomass of Jiangsu is lower than that of Shanghai, Zhejiang and Fujian (Shanghai＞Zhejiang＞Fujian＞Jiangsu), while the underground biomass is the highest. In addition, the underground biomass of Jiangsu is higher than the aboveground biomass of itself. This biomass allocation pattern may be caused by the adverse growth conditions in Jiangsu. S. alterniflora needs to invest more resources in reproduction to adapt to the adverse environment, and under the same environmental conditions, the resources available to plants are certain, more biomass allocated to reproductive components will inevitably lead to less biomass allocated to nutritional components.