Taken the pore structure effects into account, a mathematical model to describe the interaction of mass transfers, the chemical reaction and the pore structure in the gas sensitive porous medium is presented and solved. The properties of the mass transfers and the reaction characteristics of the gas-sensitive porous system are analyzed. The effects of pore size distribution and porosity on the concentration field of detected gas and the effective utilization degree of the porous matrix are provided. The results indicate that the Thiele number, which can reflect the relative magnitude of chemical reaction rate and gas diffusion velocity in nature, is the main basis for judging the effects of various parameters. It usefully reproduces the observed effects of pore structure and reaction temperature on diffusion and chemical reaction response, showing that the gas sensitivity and the effective utilization coefficient of the gas sensitive porous medium can be controlled by adjusting key parameters.