In this paper, the authors analyzed the variation law of visible light, thermal infrared band and mid-infrared band of FY geostationary satellite for sea fog, clouds and sea surface (clear sky) in Taiwan Strait, which was based on a lot of experimental analyses by using different phases of satellite data, combined with the visibility data of automatic meteorological stations. On such a basis, reflectivity threshold was used to separate sea fog and cloud from sea surface, and brightness temperature threshold was used to separate sea fog and low cloud from middle and high cloud. In addition, night sea fog was automatically identified by the normalized difference index of mid-infrared and thermal infrared band. Finally, the automatic monitoring software system of Taiwan Strait sea fog was established, and surface observation data were used to examine the precision of remote sensing monitoring. The research results show that FY geostationary satellite could make up for the deficiency of Polar Orbit Satellite in time resolution, and it has a good performance on the dynamic monitoring service of Taiwan Strait. A comparison shows that the remote sensing monitoring results of sea fog are in accordance with observation results, and the monitoring accuracy is more than 70% in daytime. Night time accuracy is lower than that of the day time, and there exists limitation in the separation of sea fog and low cloud.