Abstract: In this paper, the thermal barrier coating with double ceramic layer structure was prepared on the sample by atmospheric plasma spraying. The surface coating and intermediate coating were Gd-Yb modified YSZ and YSZ, respectively, and the metal bonding coating was NiCoCrAlY. After simulating real engine operating condition gas test, black spots appeared on the surface coating. In order to find out the cause of black spots, the surface morphology, internal microstructure, and composition of thermal barrier coatings containing corrosion spots by optical microscope, laser ablation mass spectrometry. etc, were analyzed. Factors such as mold spots, carbon deposits and metal particle inclusions were firstly excluded. The results show that in humid and HCl weak acid environment, a large number of Ni, Co and other elements in the metal bonding layer are corroded, the formed Ni²⁺, Co²⁺ and other free ions diffused and infiltrated into the ceramic coating to form round ion-diffused zones. The ion-diffused zones then became black spots during later heating process. Finally, the problem reproduction experiment is also carried out, and the black spot phenomenon is reproduced on the surface of the sample prepared under the same technological conditions by using the method of damp and heat test. It is verified that in the wet and hot environment, the underlying elements such as Ni, Co will spread into the ceramic surface from the inside out due to weak acid corrosion, resulting in the appearance of black spots.