Abstract: Scirpus mariqueter community is a primary vegetation occuring on seabeach salt marshes, the distribution of which in Shanghai is more than 200,000 Mu. This study, the phenology and spatial distribution pattern of Scirpus mariqueter populations, was carried out at a seabeach salt marsh in Donghai Farm, Nanhui county, Shanghai. According to the altitude of salt marsh and the growing status of Scirpus mariqueter populations, three zones could be recognized, that is, zone A, the ectone of Scirpus mariqueter and Phragmites australis; zone B, the optimum area for Scirpus mariqueter population growth; zone C, the colonizing area of Scirpus mariqueter population. There were obvious differences in the phenology of Scripus mariqueter populations,due to the different habitat conditions in three zones. From the zones A to C, the spatial distribution patterns of Scirpus mariqueter populations appeared in order as random, regular and clumped or random. The distribution patterns were changed in spatial positions along with their changes in time, which also reflected the reformative roles of Scirpus mariqueter populations on the habitats of seabeach salt marshes.