The present study used beam trawl net to collect crabs by Ocean Researcher III at four sites, Wanggong, Taisi, Cigu and Jiading, in western waters off Taiwan from July 2006 to October 2008. In total, 3205 crabs were obtained, including 11 families, 22 genus, 41 species and 6 unknown species. Among these families, Portunidae contained the most species (21 species, 45¢H), followed by families Majidae (4 species, 9%), Leucosiidae (3 species, 6%) and Dorippidae (3 species, 6%). Six dominant species were Portunus hastatoides (60.1%), Portunus argentatus (13.7%), Portunus sanguinolentus (7.2%), Matuta victor (3.8%), Charybdis truncata (3.0%) and Portunus pelagicus (2.1%) contributing 89.8% of the total catch. P. sanguinolentus (35.6%), P. pelagicus (16.3%), P. hastatoides (12.0%), Calappa philargius (11.5%), P. argentatus (8.0%) and Charybdis feriatus (3.1 %) were the six dominant species (86.5%) by biomass. Spatial distributions of the benthic crabs by number were significantly different. P. argentatus was the most dominant species in Cigu, whereas in the other three stations was P. hastatoide. Among the six species, P. sanguinolentus, P. pelagicus and C. feriatus are the most important species in terms of economic value. The former appeared in large numbers in Jiading and composed 35.6% in weight of the total catch from all sites, while the latter frequently occurred in the other three sites and contributed 16.3% to the overall sample weight. Moreover, P. sanguinolentus was the dominant species in terms of weight in Jiading, but the rest of three sites dominated by P. pelagicus. P. hastatoides occurred mostly in the substrate with very fine sand. P. sanguinolentus increased in number and weight with decreasing of salinity and water depth. P. argentatus had a narrowest optimum temperature range from 24.3 to 28.3¢J.