A multi-scale model of methane catalytic combustion was built by a series of balance equations and diffusion equations, and these equations were solved through the computational fluid dynamics (CFD) software. The difference between this work and previous model is the diffusion process in catalyst coating was considered. By analyzing the methane conversion, temperature distribution and mass fraction contours of every component, the performance of multi-scale model was compared with that of the pure CFD model without diffusion. The effects of diffusion, methane concentration, flow rate on the methane conversion and temperature distribution of monolithic reactor were also evaluated and discussed by the multi-scale model. The multi-scale model showed better accuracy than the pure CFD model without diffusion process. Different methane concentrations and gas flow rates had enormous effects on the methane conversion and temperature. Therefore, it was beneficial to the reaction process to adjust the methane concentration and gas flow rate appropriately.