On the basis of the bottom trawl survey data from spring (May), summer (August) and autumn (November) in 2010 to winter (February) in 2011 in the waters of Zhongjieshan Islands, we studied the resource density and community diversity of crab. Twelve species belonging to 7 genera, 8 families of crab were caught. There were 5 dominant species: Charybdis bimaculata, Charybdis japonica, Carcinoplax vestita, Eucrate crenata, Portunus trituberculatus. Among them, Charybdis bimaculata and Charybdis japonica were major dominant species. For percentage of the number of species, the eurythermal and euryhaline species both occupied the dominant positions. Both the biomass density and the number abundance density in autumn reached the maximum, and in winter reached the minimum. Otherwise, the biomas density and the number abundance density in autumn, were especially different in spring and winter (P<0.05) respectively. The Margalef richness index (D) is 0.17-0.73, Shannon Wiener diversity index (H′) is 0.19-0.71, and Pielou evenness iddex (J′) is 0.21-0.58. There were significant differences in the diversity indices among 4 seasons(P<0.05).