The thermal effluent discharged from nuclear power plants can affect the offshore ecosystem change. The ability of measuring sea surface temperature in high resolution with Airborne MSS thermal spectral band(8.5µ°12.5µ) and Landsat ETM+(10.4µ°12.5µ) gives us an information of spread range of thermal effluent. The sea surface temperature (SST) mapping from the Landsat thermal spectral band was carried by NASA model using pre-launch calibration constants. Remote sensing devices record radiance as a digital number (DN). DNs are related to radiance linearly, and can be converted using a slope-intercept equation based on the DNs of two targets of known radiance. Given the radiance, atmospheric corrections need to be made. The corrected radiance then can be converted to temperature. After that we conducted post-processing to calibrate with the real water temperature measured at the exhausting port of power plant. The SST information can be used as one of major factors for analyzing the impact of the fish farm damage around the nuclear power plants. Every season from November 1999, this research has been conducted to investigate the extent of diffusion of thermal effluent discharged from KoRi, UlJin and WolSung Nuclear Power Plant located at the coastline of the East Sea of Korea