Abstract: The environmental impact assessment of nuclear power plants is the process of analyzing, predicting and evaluating the possible environmental impacts caused by the construction projects of nuclear power plants, and then putting forward measures to prevent and reduce the impacts. In the practice of environmental impact assessment of nuclear power plants, the assessment elements are very wide, not only focusing on the site characteristics, meteorology, hydrology and other aspects, but also paying great attention to biodiversity protection, which is mainly reflected in the standardization of assessment system, assessment factors and analysis and demonstration process. Based on this background, it was pointed out that the factors affecting biodiversity in nuclear power plant environmental assessment included entrainment effect, thermal discharge, residual chlorine, seasons and other factors. The problems of environmental impact assessment of nuclear power plants were analyzed, such as the lack of relevant regulations in practice and the limitations of temperature rise assessment methods. It was suggested that the environmental impact assessment of nuclear power plants should comprehensively consider the related factors affecting biodiversity, establish a sound legal and standard system, and clarify the discharge standards of residual chlorine and thermal drainage. Other suggestions such as making up for the limitations of evaluation methods by remote sensing monitoring and carrying out post-evaluation timely were also proposed.