Solid oxide fuel cells convert chemical energy into electrical energy directly through electrochemical methods, and the residual stress in the preparation process endangers its reliability. In this study, the cosine function is used to approximate the non-flat cathode-electrolyte interface, and the effects of different wavelengths on residual stress and failure probability are clarified. The results show that the electrolyte is under compressive stress and the cathode is subjected to tensile stress at the non-flat interface. The compressive stress of electrolyte is the largest at the trough, while the tensile stress of cathode is the largest at the peak. The smaller the wavelength, the stronger the stress fluctuation. In the process of anode reduction, the failure probability of cathode is the largest. The longer the wavelength, the smaller the residual stress and the smaller the failure probability.