Based on the data taken from fishery resource surveying of the sea areas around Qinshan Nuclear Plant during spring (2010-05), summer (2010-09) and winter (2009-12) and the mathematical simulation results of thermal discharge diffusion in Qinshan Nuclear Plant, we studied the temporal and spatial distribution pattern of fish assemblies, the dominant species, and the contributions of dominant species to fish quantities in the water of Qinshan Nuclear Plant. The results showed that the density of fish in terms of individuals was highest in summer (22.10×10³ ind/km²), intermediate in winter (10.52×10³ ind/km²) and lowest in spring (5.55×10³ ind/km²). However, the seasonal variation in fish quantities in terms of weight was different from other waters. The fish density in terms of weight was highest in winter (66.46 kg/km²), intermediate in summer (59.06 kg/km²), and lowest in spring (33.80 kg/km²).The seasonal variation in fish resource quantities was different to other seas; the densities in terms of weight were higher in winter than those in spring and summer. This was probably related to thermal discharge from the plant making the proximal sea regions warmer than the surrounding sea waters, which could benefit the fish assemblies in winter because of a warm pool effect. Thus, fish assemblies aggregated in the thermal plume of the plant to overwinter. Horizontal distribution of thermal discharge has an important effect on fish distribution patterns. The fish density in the thermal discharge seas in summer was generally lower than other seas and was the opposite in winter:fish may have been stranded in the hot thermal discharge plume areas, thus showing a higher fish density. Thermal discharge has different effects on fishes with different adaptabilities to temperature; the warm temperature species that are adapted to relatively low temperature, such as Collichthys lucidus, which has high thermal tolerance, became the dominant species in the thermal discharge-impacted seas in summer. The adaptability to temperature of the dominant species of fish determines the distribution characteristics of fishes; the most important dominant species in winter was , whose contribution rate on the mantissa was up to 45.02. They aggregated densely in the hot thermal discharge plume area, which caused the fish density in the thermal discharge seas to be greater than the surrounding waters. The thermal discharge-inducedchange in the fishes' environment led to the formation of new wintering grounds, which would be likely to form a new fishing season, leading to changes in local fishery attributes.