Abstract: A gas diffusion contrast experiment between tectonic coal and undeformed coal had been carried out. The results show that the gas diffusion rate of the tectonic coal increases more rapidly in the early and also decay more quickly in the late compared with the undeformed coal; the diffusion rate of tectonic coal is larger than that of undeformed coal in the whole process of diffusion. The experiment indicated that the diffusion coefficient is a variable gradually decaying with the increase of time. Therefore, the expression of dynamic diffusion coefficient is proposed and dynamic diffusion coefficient new model is established. Through the verification, the new diffusion model can accurately describe the gas diffusion process of different types of tectonic coal all the way and the fitting precision is higher than that of classical model. It means that the new diffusion model is more precise and has a wider range of application.