In the production line of glass sheets, the 8%Y2O3-ZrO2 thermal spray coatings have put into practical uses. These coatings have under layers of metal Cr3C2-Ni/Cr cermets, to improve their bonding strength. In forming process of glass, non-oxygenated atmosphere containing sulfur dioxide is selected continually to improve the surface condition of glass sheets. Degradation and pealing of these coating have been observed frequently due to increasing of SO2 concentration. In this study, effects of SO2 on decay durability of the 8YZ coating having meta cermet under coat are examined. Interactions between the atmosphere and the top-layer or the under layer are clarified individually by some basic examinations and analysis. It is clarified that peeling of the bi-layer coating was occurred at the boundary region between top coat and under coat. By exposure test of the coated sample and some powders for N2-SO2 at 113K, following results obtained, 1) Some cracks and fine streaks are observed also, in the bottom region of the ZrO2 top layer after the exposure test of coated sample.. 2) Main components of these streaks are Cr and S. 3) Sulfur contents of Cr3C2 cermet and Cr3C2 are increased remarkably by the exposure test. 4) By the exposure, Cr3C2 can be converted into a Cr2O3 or a CrSx. due to reaction with SO2. As peeling of the coating on carrying roll is induced by oxidation and sulfurization of Cr3C2, the under layer of Cr3C2 cermet is not suitable especially as its under coat.