The work aims to design ZrB2-SiC functionally graded materials (FGM) on C/C composite substrate. Numerical simulation was performed to the residual stress of plasma sprayed ZrB2-SiC FGM by virtue of Ansys software so as to analyze the effects of composition distribution exponent p and gradient layer thickness t on the residual stress of gradient coating. Through thermal stress analysis based on cantilever beam theory, residual stress of the coating contacting the substrate when substrate thickness differed from λ was calculated. According to the simulation analysis results, the FGM layer thickness had little effect on the axial compressive stress in the interface between coating and substrate, while radial compressive stress and tangential stress increased as the coating thickness increased. Serious stress concentration was present in the marginal area and might lead to interlaminar failure. On top surface of pure ZrB2 coating, radial compressive stress was the main stress form, which gradually decreased to zero in the radial direction, suddenly became tensile stress on the edge and decreased as p increased. Compared with analytical method, residual stress of the coating interior contacting the substrate calculated in two methods gradually decreased as λ increased, conforming to the stress distribution principle of coating interior. According to optimization design, optimal thermal stress variation and mitigation effects could be obtained provided that the compositional gradient exponent p=4 and the coating thickness d=0.1～0.2 mm. Analytical solutions based on the cantilever beam theory can be used to evaluate thermal stress favorably and verify correctness of the simulation.