Ommastrephes bartramii distributed in the northwest Pacific is one of the important fishing grounds.The environmental factors are the important content of the study on fisheries oceanography, which is also helpful to understand the forming mechanism of fishing ground and creating some possibilities for providing certain scientific advice for the production of Chinese squid jigging fishery. Based on the fishing data collected by Chinese squid jigging fleets in the north Pacific Ocean (150°E-170°E), the temperature data between August and October from 1998 to 2008, the water temperature at different layers ( T₀, 55 m, 105 m) and temperature structure (0-55 m and 55-105 m) in the fishing ground of Ommastrephes bartramii are analyzed. The information values of different classification attributes for environment factors are calculated by means of the information gain technology (IGT). The results show that the T₀ in fishing ground seems to be varied seasonally from August to October. The water temperatures at 55 m and 105 m are lower and the temperature gradient at 0-55 m is higher in September. Based on the IGT, the results show that the key water temperature factors are the temperature gradient between 0-55 m, the water temperature at 55 m, the T₀, the water temperature at 105 m and the temperature gradient at 55-105 m in turn.