The work aims to explore causes of mildew by analyzing ingredients of the coated glass surface of which coating is prepared on glass surface by magnetron sputtering. Elements of mildew-free area and moldy area on coated glass were analyzed with SEM-EDS and XPS. The analysis results were compared with those of the samples for land transportation. Main causes of mildew were analyzed and discussed. The coated glass for marine transportation was analyzed in depth, changes in elements distribution as a function of depth were tested. Star white spots appeared on the coated glass, fluorine was detected on the coated glass during XPS test, fluorine content was 0.12%, diffusion depth was about 11nm; fluorine content of white spots was higher, 1.07%, diffusion depth was about 65 nm; and Na element has been diffused to the surface of samples. During the course of marine transportation, coated glass is long exposed to fluorine substances from the sea, the protective SiO2 on the top layer of the film is eroded, peeling of the film causes the coated glass to be exposed to a great deal of water vapor. Soluble silicate on surface layer is hydrolyzed and destroyed, sodium hydroxide forms and leads to massive glass mildew.