This　paper　investigates　the　thermoelectric　characteristics　of　cross-flow　planar　type　solid　oxide　fuel　cell　(SOFC)　with　natural　gas　as　fuel　by　using　a　three-dimensional　numerical　model.　The　results　reveal　that　temperature　and　reactant　concentration　increase　gradually　along　the　direction　of　fuel　gas　flow,　and　the　reactant　concentration　increases　in　the　first　and　subsequently　decreases.　In　addition,　the　lower　the　temperature,　the　higher　ideal　electromotive　force　is　as　well　as　the　less　actual　output　electromotive　force.　The　hydrogen　concentration　is　positively　correlated　with　the　current　density　and　the　ideal　electromotive　force.　However,　increasing　the　mass　flow　continuously　beyond　the　reasonable　range　can　decrease　the　current　and　electrochemical　reaction　intensity.　Variation　in　wall　thickness　was　also　simulated　and　found　that　increasing　the　thickness　would　result　in　higher　intensity　of　electrochemical　reaction　and　increased　current　density　but　at　the　cost　of　low　efficiency　in　SOFC.　Thus　an　optimal　design　can　make　a　balance　between　fuel　utilization　and　output　power　of　SOFC.　©　2018　American　Society　of　Mechanical　Engineers.　All　rights　reserved.