Abstract Fuel cells convert the chemical energy present in fuel (e.g., hydrogen) into electrical energy with high efficiency, low pollution and low noise. Of the various types of fuel cells, the solid oxide fuel cell (SOFC) was developed specifically for power plants and residual power systems. SOFCs are classified into three categories based on their shape: planar, cylindrical and flat-tube. The flat-tube SOFC (FT-SOFC) exhibits the advantages of ease in sealing, low stack volume and low current-collecting resistance. However, due to its weak strength, the FT-SOFC may get deformed or break during the manufacturing process. To improve the cell strength, the cell support must be thickened. However, as the support thickness is increased, the electrons must travel a longer distance, which leads to an increase in the electrical resistance. In another method, the hydrogen channel diameter can be reduced for the strong strength. But, it may lead to a corresponding decrease in the hydrogen mass transfer rate. In this manuscript, we study the performance of several FT-SOFC designs and suggest the better design. The numerical analysis for the FT-SOFC incorporates several physical phenomena such as gas flow, heat transfer and electrochemical reactions. The governing equations (i.e., mass, momentum, energy and species balance equations) are calculated for heat and mass transfer. The open circuit voltage, activation polarization, ohmic polarization and contact resistance are simulated simultaneously. The experimental results are compared with the numerical data for the purposes of code validation. The current density and temperature distribution are then investigated on the SOFC surface. The average current density decreases by 14.6% if the hydrogen channel diameter is narrowed by 50%, and by 10.2% if the support thickness is increased by 50%. Based on these results, we present a design for a stack of FT-SOFCs.