AlN ceramics have high hardness and brittleness, and it is difficult to be sintered and dense. As a smelting vessel, it is damaged by high-temperature deformation or thermal shock caused by temperature change. AlN/YAlO3 composite ceramics were prepared by pressureless sintering method by adding YAlO3 as a particle reinforcement phase, and the thermal shock resistance of AlN/YAlO3 composite ceramics at different temperatures was investigated. The phase structure, fracture morphology, and surface morphology of AlN/YAlO3 composite ceramics before and after thermal shock were analyzed, and the mechanism of thermal shock damage was elucidated. The results show that the addition of YAlO3 can promote the sintering and increase the density to 98.37% of AlN ceramics. The flexural strength and thermal shock resistance of AlN/YAlO3 composite ceramics are improved due to the grain refinement. Especially in thermal shock experiments at higher temperatures, when the thermal shock temperature rises to 600 ℃, the flexural strength and residual strength ratio of AlN/YAlO3 composite ceramics are significantly higher than those of AlN ceramics, indicating that the addition of YAlO3 can effectively improve the thermal shock resistance of AlN ceramics. It is mainly attributable to microcrack toughening, crack deection and branching behavior slow down the reduction of flexural strength of AlN/YAlO3 composite ceramics. Moreover, when the thermal shock temperature reaches 1 000 ℃, Al2O3 oxidated by AlN reduces severely the flexural strength of AlN/YAlO3 composite ceramics.