To study the cost structure and economic performances of Penaeus vannamei farming in Shanghai region, about 135 hectares of fanning ponds, which are scattered in Nanhui, Fengxian and Jinshan districts belonging to Shanghai City have been investigated. .By analyzing the data collected, the paper concluded as follows. Firstly, the ratio of input to output is 1:1.3 in the P. vannamei fanning. Secondly, the market profit rate of P. vannamei farming is about 26.1% . Thirdly, the marginal security rate of operation is 68.8. The results show that the overall operation status of P. vannamei fanning is fairly secure. The study of farming cost structure shows that the fixed cost and the variable cost account for 12. 8% and 87. 2% of the total cost respectively. The results indicate that the farmers should pay more attention to the reduction of the variable cost for increasing the P. vannamei farming profits. The sensitivity analysis of the factors, including market price and others, shows that the sensitivity coefficients of the market price, the variable cost, the fixed cost and the output are 4.5,-3.1,-0.23 and 1.43, respectively. The sensitivity coefficients of the above factors show that the benefits of P. vannamei farming is influenced largely by the market price and the variable cost per unit. The author suggests that the total farming scale should be programmed to prevent the failure in the profit increase due to the expanding of fanning ponds. The author thinks it is very important to build a sustainable P. vannamei farming mode with respect to protection of environment and the improvement of profitability. In addition, the scientific methods should be introduced to the farmers whose level of education and operation is low.