Based on the mathematical simulation results of thermal discharge diffusion and the data taken from fishery resources surveying of the adjacent sea areas of Qinshan Nuclear Power Plant during spring (May,2010), summer (Sept.,2010) and winter (Dec.,2009), we divided the fish community distribution through cluster analysis method, explored and analyzed the effects of thermal discharge from Qinshan Nuclear Power Plant on fish community distribution of the adjacent sea areas,from the aspects of spatial distribution and species composition, species number and diversity of different communities, etc. The result showed that the adjacent sea areas of thermal discharge of Qinshan Nuclear Power Plant were divided into two communities in spring, summer and winter, namely:the sea areas affected by thermal discharge (i.e. community I, hereinafter referred to as the inside; located near the outlet of Qinshan Nuclear Power Plant, thermal discharged into the water made water temperature rise, the water temperature decreased outward diffusion) and the sea areas outside of the thermal discharge (i.e. community Ⅱ, hereinafter referred to as the outside). Differences of fish community structure showed differences of the characteristics of fish species quantity and diversity index were consistent in spring and summer, the outside was higher than inside, quantity density had a large difference, and the differences were significant in summer and winter, showing distinct characteristics. The quantity of fish species outside (14 kinds) > inside (6 kinds) in spring, the average value of individuals and weight diversity index (H_n') was similar, outside (2.30 and 1.93) > inside (1.76 and 1.56), quantity density had large difference, individual density outside (1.95×10³ ind/km) > inside (0.88×10³ ind/km), and weight density inside (6.14 kg/km²) > outside(2.26 kg/km²), mainly related to thermal discharge in spring affected fish spawning, fish assembled inside and had higher weight; similar to spring, in summer, the quantity of fish species, individuals and weight diversity index, individuals and weight density were all outside(11 kinds, 1.76, 1.92, 2.57×10³ ind/km and 9.06 kg/km²) > inside(9 kinds, 1.75, 1.65, 1.98×10³ ind/km and 3.67 kg/km²), mainly because the temperature of the sea water in summer was higher, thermal discharge into the sea water changed the characteristics of fish community inside, showed inside was lower than outside; and the winter was opposite to summer, all indicators were inside(15 kinds, 1.61, 1.86, 1.09×10³ ind/km and 8.64 kg/km²) > outside(7 kinds, 1.24, 1.13, 0.84×10³ ind/km and 4.72 kg/km²), mainly because the temperature of the sea water in winter was lower, probably related to thermal discharge 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. Thermal discharge has different effects on fishes with different adaptabilities to temperature; some warm temperature fishes can be adapted to relatively low temperature, so the quantity of warm temperate fish species and fish species (8 kinds and 15 kinds) in the adjacent sea areas of thermal discharge were all the highest in winter among the three seasons, which was related to species distributed densely in the hot thermal discharge plume areas, thus formed the phenomenon that fish species in the adjacent sea areas of thermal discharge had more kinds than other communities.