Gas concentration measurement is crucial in the process industry. The measurement principle of non-dispersive infrared (NDIR) sensors is based on the difference in the absorption intensity of infrared light for different gases. It is widely used to measure CO2 and N2O concentrations for reducing the influence of environmental factors. But, the inhomogeneous gas diffusion in NDIR sensor chamber generates principle errors. It is necessary to determine the accurate time when CO2 and N2O reach stable diffusion within the gas chamber to reduce errors and improve the measurement accuracy. In this article, a Gaussian diffusion model is proposed to predict the gas stable diffusion time in the gas chamber of the NDIR sensor to correct gas concentration. The effectiveness of the proposed Gaussian diffusion model is evaluated by the simulation experiment. Fourteen sets of simulations for CO2 and N2O under different conditions show that the fitness of the proposed Gaussian diffusion model is 0. 82 and 0. 80, respectively, which verifies the robustness of the proposed model. The Gaussian diffusion model between gas stable diffusion time and inlet flow velocity provides theoretical support for error correction generated by inhomogeneous gas diffusion which finally improves the measurement accuracy.