Abstract: Microstructure of the thermal barrier coatings is a key factor affecting its service performance. The microstructure and thermal shock behavior of scandium yttrium co-stabilized zirconia（ScYSZ） thermal barrier coatings with sub-micron and nano-sized bimodal structures were investigated. The results show that the thermal shock life of the ScYSZ coating with sub-micron structure is 286 times at 1300 ℃. While the bimodal-structured coating with nano-sized unmelted particles/layered structure can significantly improve the thermal shock life of the coating, which reaches 376 times. The microstructure of sub-micron coating is relatively dense, and the vertical cracks through the coating thickness are easily to generate during the high-temperature thermal shock test. However, the propagation of vertical cracks in the nano-coating are terminated by the stress release encountering the loose nano-unmelted particles. The main failure mode of the nano-coating is the spot spallation.