This study numerically investigates methanol steam reformer design using the COMSOL software. The reformer is heated with internal heating tubes (HTs). The effects of the reformer shape, the heating tube arrangement and heating rate are studied. Results show that a divergent reformer shape has the highest methanol conversion (68%) due to slower average flow rate of the reactants, longer residence time, and more heat absorption. For fixed heating rate, increasing the number of HTs increases the methanol conversion rate by up to 14.8% due to better heat transfer. Furthermore, methanol conversion can also be enhanced with increasing heating rate and placing HTs towards reactor center. The optimal design of a divergent tube with a divergent angle of 5° and 8 HTs has a maximum conversion rate of 94.5%. The results of this study are helpful for engineers working on designing an MSR with high-methanol conversion rate.