A 2D numerical simulation is conducted on the steam reforming reaction in a plate microreactor by applying the general finite reaction rate model in the CFD software FLUENT and a detailed surface reaction kinetics mechanism. Catalyst space velocity(CSV) and gas space velocity(GSV) inlet mixture impact on the reaction is discussed. During the calculations, the space reaction effect is ignored and only the reaction of CH4 on catalytic surface is taken into account. Calculation results show that lower CSV or GSV can achieve highefficiency conversion of CH4 and H2 output; besides CSV and GSV, channel height is an important factor for the reforming performance of plate microreactors.