A gas-solid coupling model is designed, which uses microwave heating porous medium(silicon carbide) to heat gas indirectly, aiming for the application of gas-solid model coupling and gas-solid reaction under microwave assisted heating. Finite element simulation software is adopted to build the model. The accuracy and feasibility of the gas-solid coupling model are verified by coupling simulation of three physical fields: electromagnetic field, fluid heat transfer field, free and porous media. The results show that the microwave conversion efficiency is the highest when the porosity of silicon carbide is 0.5 and the radius of quartz tube is 20 mm, and the microwave energy efficiency is above 90%.