Abstract: The rapid development of the nuclear power industry in China has led to concern over the ecological impact of thermal discharges. To obtain remote sensing and field measurement data of eight tidal states around Hongyanhe Nuclear Power Plant during spring and neap tides in summer, the unmanned aerial vehicle (UAV) thermal infrared remote sensing technology was employed to measure the high temperature rising area stipulated in China’s Seawater Quality Standard (GB 3097－1997). After that, the spatial distribution of thermal discharge as well as its influencing factors were examined. The results indicated that (1) SSTs measured during aerial surveys, corrected by a quadratic polynomial with MAE = 0.4 ℃, are helpful in estimating temperatures and identifying thermal discharges. (2) There is a similar spatial distribution of thermal discharge under the same tide state. Among different tidal states, flood slack and ebb slack tidal states are associated with increased temperature-rising areas than maximum flood and maximum ebb tidal states. Compared to the area variation of high temperature rising levels near the offshore, there is a significant area variation of low temperature rising levels far offshore. (3) In spring tide, the maximum ebb state is most conducive to thermal discharge diffusion, and in neap tide, the flood slack state is particularly problematic. (4) The tidal state has a more profound effect on thermal discharge spatial distribution than the wind field.