We addressed the influence of reclamation on community structure by comparing macrobenthic communities in a natural tidal flat and creek of a tidal flat diked in 1997. Sampling was conducted during Feb. to Nov. 2006 near Lingkun Island, Wenzhou Bay. Eight sampling plots (4 each in natural and diked systems) represented different macrobenthic habitats, including two invaded by Spartina alterniflora. In the investigation, a total of 36 species were found, belonging to 22 families, 8 classes, and 7 phyla, most of them being arthropods, mollusks and annelidas. Results indicate that after diking, species richness decreased and the composition of species also had changed. There were 32 species in the natural tidal flat, but only 27 macrobenthic species could be found in the diked tidal flat. The species composition of various macrobenthic communities, life groups and life forms on species of the macrobenthic community in various habitats, the density characters of quantitative sampling exhibited the structure of macrobenthic communities were highly related to the condition of habitats. The niche breadths of the macrobenthos species and biodiversity indices were also analyzed in the paper. Shannon-Weiner index H′ was much higher in 2(high tide level and middle tide level) of the 4 habitats within in diked and natural tidal flats. Plots with Spartina alterniflora exhibited lower H′ and J than other plots nearby which were unvegetated and similarly influenced by tidewater. Thus, invasion by Spartina alterniflora has already influenced and changed the macrobenthic community in these habitats. The similarity index Jc, paired t-tests, the hierarchical cluster of between-groups linkage method and the Non-metric Multidimentional Scaling (MDS) method reveal that the influence of tidal level on macrobenthos distribution is much stronger in the natural flat than in the diked tidal flat.