To study the microstructure changes and phase transitions of different depth areas in the YSZ coating caused by corrosion of the calcium magnesium aluminum silicate (CMAS) at high temperature, scanning electron microscope (SEM) and an X-ray diffractometer (XRD), energy-dispersive X-ray spectroscope (EDS) and electron backscatter diffraction (EBSD) were used to characterize and analyze the YSZ coating before and after corrosion. The results show that YSZ coating after high-temperature CMAS corrosion exhibits spalling, dense, light dense and obvious layered structure from top to bottom. The melting/recrystallization phenomenon occurs on the top of the YSZ coating, which causes a phase transition from initial t-ZrO₂ particles to m-ZrO₂ particles and the degree of the phase transition decreasing from top to bottom. It is also found that the CMAS-induced phase transition mainly occurs at the grain boundaries since the molten CMAS is easier to penetrate and erode along the grain boundaries of the coating.