A 3D model is developed to describe an anode-supported planar solid oxide fuel cell (SOFC), by Ansys/Fluent evaluating reactions including methane steam reforming (MSR)/water-gas shift (WGSR) reactions in thick anode layer and H2-O2/CO-O2 electrochemical reactions in anode active layer, coupled with heat, mass species, momentum, and ion/electron charges transport processes in SOFC. The predicted results indicate that electron/ion exchange appears in the very thin region in active layers (0.018 mm in anode and 0.01 mm in cathode), based on three phase boundary, operating temperature and concentration of reactants (mainly H2). Active polarization happening in active layers dominates over concentration and ohmic losses. High gradient of current density exists near interface between electrode and solid conductor due to the block by gas channel. It is also found the reaction rates of MSR and WGSR along main flow direction and cell thickness direction decrease due to low concentration of fuel (CH4) caused by mass consumption. With increasing operating temperature from 978 K to 1088 K, the current density and the reaction rate of MSR are increased by 10.8% and 5.4%, respectively. While ion current density is 52.9% higher than in standard case, and H2 is consumed by 5.1% more when ion conductivity is doubled. CO-O2 has been considered in charge transfer reaction in anode active layer and it is found that the current density and species distributions are not sensitive, but WGSR reaction will be forced backwards to supply more CO for CO-O2 electrochemical reaction.