This paper is devoted to the investigation of the steam methane reforming process in a microchannel reformer over a Ni-based catalyst. The composition of reforming products and temperature at a reformer outlet was measured experimentally as well as with the help of CFD-modeling and numerical study. The presented new direct numerical method for modeling of steam methane reforming. The study of steam methane reforming was performed for the inlet temperatures (Tin) of 600–1000 K, for Re = 10, 50, 100, and heat flux through the walls of qw = 1000 W/m2 and qw = 500 W/m2. It was found that the methane conversion in the reformer decreases with increasing Reynolds number, heat flux through the wall, and inlet temperature. For Re = 10, qw = 1000 W/m2 and Tin = 1000 K the methane conversion is 39% while equilibrium methane conversion is 63%. The temperature profiles in the reaction zone were determined. The temperature of the reaction mixture monotonically increases for all Reynolds numbers.