Based on the data from scientific fishery investigation in the waters of middle Northern Jiangsu shoal in May 2011 and November 2010, respectively, using the methods of variance and regression, the effects of bathymetry of sand ridge and tidal channel on the distribution pattern of the fishes were studied, through the analysis of the fish shape features, fish density and the index of relative importance of dominant species and the contribution of dominant species to the total population. Spatially, the distribution patterns of fish were associated with the bathymetry of the tidal channel system. The outer water of the tidal channel in spring was dominated by marine species, including Larimichthys polyactis and Michthys miiuy which migrated to the waters for spawning. Inside the tidal channel, Pholis fangi was predominant migratory fish, M. miiuy was also found in the area. In the sand ridge, it was mostly composed of adult of Thryssa kammalensis and no migratory fishes are found. In autumn, the distribution of fish species is only associated with the terrain of the bathymetry of the tidal channel system, in which it is almost composed of Protosalanx chinensis for shield in autumn. The result also shows that seasonal variation in densities of fish was closely associated with the spawning and nursery of fish community. The density of fish in terms of weight in spring (16.08×10³ ind/km²) was higher than that in autumn (10.74 kg/km²). However, the density in terms of individual in spring (5.36×10³ ind/km²) was lower than that in autumn (16.3×10³ ind/km²). Both average weight and body length of fish in spring were greater than those in autumn, which was probably associated with immigration of the adult of fish to the studied area to spawn during spring (e.g., spawning community of L. polyactisr and Eupleurogrammus muticus). In autumn, it was mainly composed of foraging juveniles (e.g., M. miiuy and P. fangi), due to partial fishes' finding shelter and feed here. In general, because of the special terrain of North Jiangsu shoal, the sea area becomes the site of spawning in spring while the nursery field in summer and autumn, which is of great significance in fisheries.