Benthic diversity is one of the important indexes to indicate marine water ecological environment. Spatial variations in benthic species in coastal zones have often been related to the geomorphic complexity. However, there have been few attempts to investigate the linkages between benthic diversity and the complexity of coastal topography in order to predict their likely responses to coastal reclamation. The focus of this research, therefore, is investigating the coastal geomorphologic features of typical bays in China and parts of the other countries, and theirs benthic biodiversity index in order to discuss the relationship between them by using the fractal dimension (D) of fractal geometry and shape index (S) of landscape ecology. A correlation model of diversity index of costal benthos and quantitative indexes of geomorphic complexity is established by multiple regression analysis. We selected typical coastal zones of Zhejiang Province as a case to discuss the influences of tidal flat reclamation on coastal geomorphologic complexity and water ecological environment using related models and measured data. The results indicated that the benthic biodiversity had significant correlations with quantitative indexes of geomorphic complexity (R2 > 0.75 (P < 0.05)). This also shown that coastal geomorphologic complexity is one of the important factors that influence the benthic biodiversity and water quality. This improved information will contribute to better sustainable development in coastal areas.