This paper presents the result of numerical simulation of methanol steam reforming in a microreactor over Cu/ZnO/Al2O3 catalyst integrated with a methanol catalytic micro-combustor. The microreactor consists of channels of 700 µm width and 20 mm length. Effects of catalyst thickness, gas hourly space velocity of steam reforming, and gas feed composition of the steam reforming channel on methanol conversion and CO generation are investigated. Simulation results indicate that hydrogen yield is enhanced by 68% when the catalyst thickness is increased from 10 µm to 100 µm. The optimal gas space velocity in the steam reforming channel is obtained at 3000 hr-1.