Four typical successional series in the marsh communities of Sanjiang Plain were selected to investigate the changes of their beta diversity. The results indicated that from the 'starting community' to the 'end community', which had the most and the least moisture level in the series, respectively, the similarity coefficient between each community and 'starting' community decreased with decreasing moisture gradient and increasing horizontal distance. The species turnover speed among the communities in each series had an increasing trend from lowland to upland. In the process of succession, the general trend was that the total number of plant species increased while the common species decreased, with the beta diversity between communities increased gradually. The analysis of succession mechanism supported the 'initial floristics composition hypothesis', and the plant Calamagrostis angustifolia would intensify its dominance in the mash of Sanjiang Plain.