The membrane reactor about methane reforming of CO2 (so called dry reforming) is studied by computational fluid dynamics approach. The effect of changing the number of membranes is modeled and investigated. The number of membranes for the simulation is chosen with two, three, four, five, six, eight and nine membranes. The separation distance between each center of the membrane and the center of the reactor is fixed. Cross sections of temperature distributions and the profiles of both hydrogen and methane concentrations within a membrane reactor are shown. In addition, we obtain conversion of methane as well as that of the carbon dioxide for corresponding geometries. Even though the conversions of both methane and carbon dioxide generally decreases (likewise the production of hydrogen does), the permeated hydrogen into the membrane increases as the number of membrane increases. It turns out that the reactor equipped with more number of membranes is preferable for hydrogen selection. This information may give us a critical guideline of reactor design before constructing scaled up reactor.