We evaluated the biodiversity and community structure of the macrobenthos in Sandu Bay, China. In addition, we evaluated the response of the macrobenthos to mariculture practices. This bay is typical of many areas of China’s coastline, and is characterized by high density mariculture. We collected samples from 20 sites during nine cruises between May 2009 and February 2010. The Shannon-Wiener index of the macrobenthos in Sandu Bay ranged from 1.45 to 3.22 (mean: 2.40). The Margalef richness index varied from 0.99 to 2.41 (mean: 1.68). The Pielou evenness index changed within the variation from 0.76 to 0.93 (mean: 0.88). The Shannon-Wiener index and Margalef richness index were generally much higher at control sites or sites near the mouth of the bay. A total of five macrobenthic groups were identified at an arbitrary similarity level of 30%, based on samples collected in August in Sandu Bay. The community structure was similar at neighboring sites or at sites with similar mariculture operations. ABC curve analysis suggested that the macrofaunal communities were disturbed in May and August, but not in February and November. Of the environmental variables we measured, dissolved oxygen levels at the surface and sea-bed, acid volatile sulfide content, and sediment oxidizing redox potential were most closely related to the structure of the macrobenthic assemblage (<0.01).