Abstract: Plasma sprayed Al2O3-TiO2/NiCoCrAlY coatings with a gradient distributed composition or non-gradient distributed compositions were prepared on ZL104 aluminum substrate.In order to study the thermal shock resistance and thermal shock failure mechanism of Al2O3-TiO2/NiCoCrAlY coatings,the samples were heated to 400 ℃ and hold a certain time then cooled to room temperature by quenching.The results stcow that the thermal shock resistance of gradient coating is much better than that of non-gradient coatings.The main cause of coating flaking-off is due to the thermal stress caused by different thermal expansion coefficients.The gradient distributed composition would release the stress in some extent and it is also of benefit to thermal-shock resistance of the coatings.After heating and cooling,the samples are bent because of the differences of dilation coefficient and heat conductivity between coating materials and substrates,or the plastic deformation of aluminum substrate.The deformation cause a residual strength stress in the coating and reduced its thermal shock resistance.