After being introduced into China's coastal zone, the exotic species, Spartina alterniflora, has resulted in a series of ecological risks and seriously influenced the structure and function of the native ecosystem. Understanding the invasion mechanisms of S. alterniflora is the theoretical basis for its effective control. The estuarine wetland in the Yangtze Estuary, China, is a typical heterogeneous tidal flat with a variety of habitats. In this study, the effects of habitat heterogeneity and ortet density on the colonization, growth, and dispersal of S. alterniflora were studied using field experiments. The results were as follows:1) habitat heterogeneity and ortet density have significant effects on the survival rate, plant height, and population growth rate of S. alterniflora (P < 0.01); 2) at the end of the growing season, the survival rate and height of S. alterniflora in the vegetation area were significantly higher than that in the mudflat (P < 0.05). In addition, the height and population growth rate of S. alterniflora in the muddy tidal flat were significantly higher than that in the silty tidal flat (P < 0.05); 3) the invasion of S. alterniflora in the vegetation area was not limited by ortet density. The growth rate of the S. alterniflora population in vegetation area decreased significantly with increased ortet density (P < 0.05), but the plant height had no significant difference (P > 0.05). In addition, only the higher density S. alterniflora rhizomes could invade the mudflat successfully; 4) the sediment disturbance regimes, flooding time, and flooding depth are the key environmental factors that affected S. alterniflora survival and growth. This study enhances the understanding of S. alterniflora invasive mechanisms in coastal wetlands, and provides a scientific basis for the control of S. alterniflora, as well as the protection, restoration, and management of the coastal zone in China.