The work aims to get the structure evolution mechanism of nano ceramic coating during gradient thermal cycle by preparing NiCoCrAlYTa bonding layer on nickel-based superalloy (k417) by low temperature-high velocity oxygen flame (HVOF) and nano-7YSZ ceramic coating on the bonding layer by air plasma spraying. Gradient thermal cycle test was carried out on nano-7YSZ TBC with a flame tester to simulate service condition of thermal barrier coating (TBC) in turbine engine. Interface temperatures in TBC were calculated based on one-dimensional model of steady heat conduction. Provided with 40 thermal cycles, the coating subsurface was subject to sintering densification, while base coating of the ceramic layer reserved the original structure. As the thermal cycle number increased to 460 times, entire section of the ceramic layer was subject to sintering densification. The coating sintering densification is mainly affected by temperature. When isometrical grains in the coating contact and form crooked neck, the grains grow slowly since the neck bears static stress in horizontal direction only and diffusion rate of atoms in the grains is slow. However, when non-isometrical grains in the coating contact and form crooked neck, the grains grow quickly since shear force in direction of large grain is present on the neck and the diffusion rate of grains is accelerated.