A micro-channel reactor with circular cross section was numerically studied. Inside the inner cylinder and the annulus section, steam reforming and oxidation reactions were occurred, respectively. With the variation in diameter of the annulus section along the reactor length, the effect of diameter changing was also studied. In this case, outer section is an incomplete cone. The results showed that conical annulus (right inlet) micro-reactor (when the diameter of the cone decreased along the reactor length) represents higher temperatures and conversions. Then, influences of some parameters were considered in this micro-reactor. With increasing some parameters such as inlet temperature and the steam to carbon ratio of inlet flow, methanol conversion increases, and increasing some other parameters such as flow rate, solid thickness and porosity of bed leads to the methanol conversion decreases as well. Effect of various diameters in this micro-reactor was considered. Also when oxidation reaction happened inside outer cone, the better results was represented. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.