Abstract: Based on the situation that the existing domestic temperature control standards are not performable, study on one of the key parameters of thermal pollution control standards-the maximum temperature limit of thermal discharge was conducted in this paper.The upper incipient lethal temperatures (UILT₅₀) of different tested species were used as the main basis of determination of maximum temperature limit of thermal discharge, with using the representative marine lives in adjacent waters of a typical northern coastal nuclear power plant site as the research objects.Combined with "regulatory research method" and "extreme temperature forecast method", the recommended values of maximum temperature limit of thermal discharge are as follows:31℃ in winter, 32℃ in spring and autumn, and 34℃ in summer.