Abstract: Environmental barrier coatings (EBCs) are susceptible to corrosion by molten calcium-magnesium-aluminum-silicate (CMAS) deposits during high-temperature service. Investigating the corrosion behavior and mechanisms of the EBCs under the CMAS attack is of significant importance for assessing their corrosion durability and enhancing their service life. This study investigates the CMAS corrosion behavior and mechanisms of the EBC of yttrium monosilicate (Y₂Si₂O₅, YMS)/mullite/silicon system prepared by atmospheric plasma spraying at 1300 ℃. The results indicate that the YMS layer gradually dissolves into the CMAS corrosives attached to its surface at elevated temperature. This thermochemical reaction leads to the precipitation of apatite at the reaction front. The formation of thin and dense apatite layer can impede the progression of thermal corrosion to some extent, resulting in a parabolic characteristic of corrosion kinetic process of the YMS layer. After 100 h of CMAS exposure corrosion, the YMS layer is almost completely consumed.