Abstract The suitable ratio of methane to oxygen is a critical selection to optimize the solid oxide fuel cells performance under internal catalytic partial oxidation reforming. In the current study, a design of experiment (DOE) with the full factorial analysis was employed to determine the optimum peak power density (PPD) as the objective function based on the flow rates as the decision variables. The response surfaces of PPD and its contour were presented in terms of the levels of the methane and oxygen flow rates. However, the low flow rate ratio of O2 to CH4 maximizes the PPD, the high risk of carbon deposition is occurred. The optimum PPD value was determined through the superposition of contour plots for regions with Reynolds (Re) number of fluid flow around 10 and O2/CH4 ratios among 0.2–0.4. The electrochemical experiment testing illustrated a stable performance of the SOFC in the optimum condition of the fuel flow rate after 120 h testing time. Furthermore, the scanning electron microscopy revealed no visible trace of carbon and crack on the anodic surface of the cell.