The invasive species of Spartina alterniflora, as an 'ecosystem engineer’ was introduced into many places in China, now, had rapidly and widely invaded into the Chongming Dongtan wetland since 1990s. Microorganisms are important components of wetland ecosystems, performing a range of vital ecosystem functions. But, we have not known how microorganisms have an influence on the invasion of Spartina alterniflora in Chongming Dongtan. In order to study the bacterial diversity and abundance in rhizosphere of invasive plants Spartina Alterniflora growing in different tidelands of Chongming Dongtan Wetlands for different seasons, we selected 10 samples collection points, which distributed on the tidal zones with plant and the blare flat zone without plant in Chongming Dongtan wetlands. The tidal zones contain low-tide zone, mid-tide zone and high-tide zone. Total DNA was extracted from soil samples, and 16S rRNA gene-based PCR was performed. A comparative study of diversity of microorganisms in rhizosphere soils of invasive exotic species ( Spartina alterniflora ) and two native species ( Phragmites australis and Scirpus mariqueter ) was conducted by denaturing gradient gel electrophoresis(DGGE) of these PCR products, representing microorganisms in rhizosphere soils.. Results showed that diversity and abundance of bacterial community were different in the rhizosphere of Spartina alterniflora, Phragmites australis and Scirpus mariqueter in the low-tide zone, mid-tide zone and high-tide zone in Chongming Dongtan wetlands.. We found that, in summer, rhizosphere bacterial communities in mid-tide zone had higher abundance than those in low-tide zone and high-tide zone (P = 0.021 < 0.05). A higher diversity of bacteria in the rhizosphere soils of these plants was observed in summer than in other seasons. The average diversity index of bacterial community was calculated and was found to be the highest in mid-tide zone (H = 4.20). The abundance and diversity of bacterial community in invasive species Spartina alterniflora rhizosphere were significantly higher than in the local plants P. australis and S.mariqueter in mid-tide zone, and the abundance and diversity of S.mariqueter rhizosphere bacteria in summer slightly higher than in other seasons. Also the abundance and diversity of S. alterniflora rhizosphere bacteria were significantly higher in tidal soils than those in the mudflat soils. Overall,these results indicated the tides had a strong influence on the abundance and diversity of the plants rhizosphere bacteria. And the exotic species Spartina alterniflora had a favorable influence on soil microbial community in wetland. We reasoned that high diversity and abundance bacteria in rhizosphere maybe were an important for the invasion of Spartina alterniflora. A higher diversity of bacteria in the rhizosphere soils of these plants observed in summer revealed that the summer is more beneficial for bacteria living in vicinity of plant roots. The fact that the flourishing Spartina rhizosphere was associated with large bacteria assemblage suggested that the high diversity and abundance of microorganisms might be identified as one of the important factors of Spartina invasion mechanisms.