Pneumatophorus japonicus and Decapterus maruadsi are the main pelagic f ishes in the East China Sea, the formation and the spatio-temporal variety of its fishing ground is restricted by the change of environmental factors. It is very significant to research the formation mechanism of central fishing ground and explore their relation for knowing the law of migration and distribution of Pneumatophorus japonicus and Decapterus maruadsi and rationally using and protecting marine fishery resources. Based on the data of marine environmental investigation in the west of 29- 32bN, 124. 5bE from 1987 to 1990, in the platform of GIS, using moderate statistic method, the study has been conducted on analyzing the relation between central fishing ground and some factors of marine environment and its alterat ion as the time and space change, then on determining the main effectual factors of fishing ground formation, and researching the mechanism of the formation of f ishing ground. On this basis, a mathematical model is established by using fuzzy set theory. Numeric examination educed that of using the grade of membership of 75% as the criterion. Using the data f rom 1987 to 1990 and that of 1997 to check the model, it is found that, applying the model to f ishing production, a good result would be gotten. The conclusion is that, the characteristics parameters, bottom temperature ranges from 19. 0 e to 21. 0 e , bottom salinity ranges f rom 33. 0 to 34. 5, and the prey biomass ranges from 137 to 409mg#m- 3 and the square of correlative coeff icient of bottom temperature and salinity can reach 0. 9935 and 0. 9988 respectively, which indicates their relation is very consanguineous. The method, that establishes the mathematical model and applies it to study the formation mechanism of central f ishing ground of Pneumatophorus japonicus and Decapterus maruadsi in the North of East China Sea so as to predict the parameters of f ishing ground as the change of time and space, will, to some extent, compensate for the deficiency of qualitative analysis.