The swimming crab, Portunus trituberculatus (Crustacea: Decapoda: Brachyura), is a large-sized benthic crab species, which is widely distributed in the coastal waters of China, Japan and Korea. FAO data show the world fishing output to be more than 380000 tons in 2010, while the figure for China alone in 2010 amounted to 350000 tons. As a result of artificial mass propagation and improved stock techniques, the farming output also reached 91,000 tons with a farming area of 30000 hectares in 2010. Therefore, the requirement of assessments and conservations of natural genetic resources has become increasingly urgent. The Haizhou Bay is located in Lianyungang coast, Jiangsu Province of China, and as one of the major fishing grounds. The bay was historically famous for the abundance of swiminng crab, but the crab population has been declining due to the over-exploitation. In order to maintain a sustainable stock, releasing of crab produced in hatcheries has been practiced annually to supplement the wild stocks. A large marine farm for swimming crab were constructed for the releasing exercise surrounding a 1700 hm² aquculture area in the Haizou Bay. In 2009 only, 5839000 individuals of swimming crab were released to the marine farm. However, these practices can cause genetic contamination to the geographically proximate wild stocks when the interbreeding ouccrs between wild poplutions and the released or escaped crabs raised in hatheries. In order to assess the genetic impact of swimming crab farming and popagation releasing on wild stocks in Haizhou Bay, 20 SSR primers designed in our laboratory were used to genetically differentiate swimming crab wild stocks and cultured stocks in Haizhou bay. There were 30 wild swimming crab samples were caught using a gill net in Haizhou Bay (near to Xiaokou village Ganyu haitou town) and 60 cultured individuals obtained from two cultured stocks from aquacultured facilties in Haizhou Bay in Nov., 2011. The results indicated that the genetic diversity of crab from wild stock was higher than that from cultured stocks. The observed heterozygosity Ho value in wild stock was 0.8509, while that in two cultured stocks only were 0.4525 and 0.5283, respectively. The one-way ANOVA showed that the genetic parameters of Ne, Ho, He and PIC in wild crabs were significantly higher than those in cultured stocks (P < 0.05), but those genetic parameters between two cultured stocks were not significantly different (P > 0.05). The Fst value among these stocks ranged from 0.1085 to 0.1448, which showed a moderately differentiated state. The gene flow Nm ranged from 1.5 to 2.0 and the genetic differentiation state was much significantly higer between the wild stock and cultured stocks than that within cultured stocks. In conclusion, the genetic resource of swimming crab in Haizhou Bay was in a good state, and the impact of swimming crab farming and propagation releasing on the natural genetic resource was not remarkerble which was probably related to short time, scale effects of crab farming and propagation releasing.