Abstract: CaO-MgO-Al₂O₃-SiO₂ (CMAS in short) deposits are often generated on the surface of in-service aircraft engine blades. In this paper, the thermal cycling behavior and associated failure mechanism of EB-PVD zirconia-based thermal barrier coatings (TBCs) with CMAS deposits were investigated. The results show that the thermal cycling life of TBCs with CMAS deposits at 1200℃ is less than 100 cycles, whereas the life of TBCs without CMAS is more than 500 cycles. CMAS deposits accelerate the spallation failure of TBCs. After 210 thermal cycles at 1200℃, about 8 μm interaction layer is formed between CMAS and zirconia ceramic layer, which is mainly due to the inward diffusion of Ca²⁺ from the CMAS deposits. A large number of transverse cracks are generated in the ceramic layer of TBCs with CMAS deposits. The failure of TBCs occurs mainly by chipping spallation of the ceramic layer.