Abstract: Solid oxide fuel cells (SOFCs) are highly efficient and eco-friendly energy conversion devices that can utilize hydrocarbon fuels such as natural gas and biogas. However, the commonly used yttria-stabilized zirconia (Ni-YSZ) anode materials are prone to carbon deposition, which can block the porous structure of the anode and lead to the degradation of cell performance and even cell failure. A dry reforming strategy using CO₂ for CH₄ reforming can shift the CH₄ fuel from coking to non-coking zones, thereby eliminating the possibility of carbon deposition from a thermodynamic perspective. This approach not only simplifies the system and reduces power generation costs, but also enables the reuse of CO₂. The reforming reaction is endothermic and can significantly affect the internal thermal field distribution within the cell. Traditional planar cells, which have an axisymmetric design, can develop localized thermal stresses on one side during CH₄ reformation at the anode, potentially causing cell warping or cracking. To address this issue, a thick anode support with a through-hole structure can be used as a catalytic layer. This modification enhances cell symmetry, creating a quasi-centrosymmetric flat-tube SOFC that allows for an isotropic distribution of thermal stresses and significantly reduces the risk of cell warping or fracture. In this study, a stack of three flat-tube SOFCs was constructed, and the power-generation characteristics of the stack under hydrogen and CH₄/CO₂ dry reforming conditions were compared. In addition, the performance changes in each cell were monitored. As per the results, the maximum power output of the three-cell stack at 750 °C on using hydrogen and dry reforming gas as fuels were 100.0 and 81.1 W, respectively, with power consumptions of the non-cell parts of the stack being 17.6 and 9.8 W, respectively. I–V curves indicated that at a CO₂/CH₄ flow of 1.2 L·min⁻¹/0.6 L·min⁻¹, the stack’s dry reforming performance approached its limit, making significant increases in output power unlikely with higher CO₂ content. At a 1∶1 CO₂/CH₄ feed ratio, the tail gas measurements indicated a fuel utilization rate of 55.8% at 18 A. During a constant current test at 15 A, after 100 h in a hydrogen environment, the stack voltage degradation rate was 0.130‰·h⁻¹. The interfacial resistance increasing from an initial 11.1 mΩ to 17.5 mΩ (growth rate: ～0.554%·h⁻¹), which is much higher than that of the stack. This indicates that stack degradation was primarily due to the increase in interfacial resistance rather than a decline in the single-cell performance. Under CO₂/CH₄ conditions, after 360 h of operation, the stack voltage growth rate was 0.0096%·h⁻¹, with the interfacial resistance stabilizing at ～31 mΩ (growth rate: ～0.0183%·h⁻¹). This further supports the excellent dry-reforming performance of the stack. Long-term operation suggested possible fuel starvation in Cell-3 (the cell farthest from the fuel inlet), which caused partial oxidation and reduced the catalytic activity. This was inferred to be the main factor in stack performance degradation. Simulation results confirmed that as the gas passes through the stack, the gas flow velocity and content decrease in subsequent cells owing to the flow channel resistance and diffusion effects. These findings demonstrate that the degradation range of the flat-tube stack under CH₄/CO₂ dry reforming is relatively small. This indicates that the flat-tube stack exhibits relatively stable methane dry reforming performance, reflecting its potential advantages and reliability in CH₄/CO₂ dry reforming applications.