Abstract: 8mol%Y₂O₃-stabilized ZrO₂ (8mol% Yttria-stabilized zirconia, 8YSZ) is widely used as thermal barrier coatings (TBCs) to reduce heat transfer between hot gases and metallic components in gas-turbine engines. However, with the increase of service temperature, it’s difficult to study the thermal performance of 8YSZ. The influence of the model size effects on thermal conductivity and ion diffusion of 8YSZ were investigated through non-equilibrium molecular dynamics simulations (NEMD). Besides, the ion diffusion and thermal transport behavior of YSZ were explored under service conditions. Using cubic 8YSZ(c-8YSZ) as the study object, the thermal conductivity was calculated for model cross-sectional areas of 4a×4a, 5a×5a and 6a×6a (Lattice constant a) at simulated service temperatures of 1273-1473 K. It was found that the cross-sectional area had a small effect on the calculated results. When the cross-sectional area of 5a×5a was selected, the thermal conductivity calculations of the models with different structure lengths of 5a, 15a, 25a, 35a, 45a, 50a, 55a, 60a and 65a were compared, and the size effect was studied to determine 5a×5a×60a as the best size of the model. The thermal transport mechanism of c-8YSZ at 1273-1473 K was also revealed, and the different phonon scattering between c-8YSZ and tetragonal 8YSZ(t-8YSZ) was also found. It was found that enhanced phonon scattering can effectively suppress the thermal transport capacity of YSZ in service, which provides a theoretical basis for improving the thermal insulation performance of thermal barrier coatings in high temperature service.