Thermal discharge has a notable influence on the composition of macrobenthic communities, yet it remains uncertain whether it also affects macrobenthic biological traits at the community level. Based on the sampling data from 12 stations near the thermal discharge outlet of the Sanmen Nuclear Power Plant between 2022 and 2024, biological trait analysis and RLQ analysis methods were used to reveal the underlying correlation between macrobenthic biological traits and environmental factors. When the species composition changes, it is expected that the traits of composition will also change, and the change in traits of composition is smaller than the change in species composition. In the feature composition, the dominant features of each station are highly consistent. In terms of species composition, the phenomenon of highly consistent species only occurs in the stations near the thermal discharge outlet. Thermal discharge altered the seasonal variations in water temperature, mud temperature, dissolved oxygen, and salinity. The temperatures of seawater and mud are the main drivers of changes in the species and biological trait compositions of macrobenthos. Gastropods and bivalves dominated the area around the thermal discharge outlet, and the abundance of macrobenthos increased significantly with increasing water temperature. The localized warming caused by thermal discharge increased the mud temperature and salinity while decreasing the dissolved oxygen concentration, thereby altering the biological trait composition. At locations with high water temperatures, trait patterns with chitinous layer profiles, small body sizes and short lifespans predominated. The fertilized eggs being protected by the parent and the prolonged stay of the juvenile in the water, which feeds on zooplankton, are the dominant biological trait patterns in terms of reproductive traits. The free crawling and burrowing lifestyle in the shallow sediment layer and the feeding pattern on detritus and animal carcasses were the dominant trait patterns.