Abstract: The FGM optimization design mainly depends on the design of gradient distribution function (GDF). By considering a power law function as GDF in the analysis, the FGM optimization was simplified to search for the optimum gradient power, i.e ., GP. The spalling analyses and optimization design of functional gradient film/substrate structure are presented in this paper. Energy release rates and stress intensity factors of the substrate crack parallel to the interface were obtained to determine the optimum GP. The relation between the thermal stress relaxation and antithermal or antioxidal properties has also been discussed.