Abstract: In the process of releasing gas from coal, the time-varying diffusion behavior caused by the change of gas concentration directly affect macroscopic characteristics of gas diffusion law of coal. The measurement of gas diffusion coefficient has always been the focus of domestic and foreign researchers. The physical and chemical essence of gas diffusion coefficient was analyzed as it presents time-varying characteristics, the commonly used experimental testing method of gas diffusion coefficient at present was mainly introduced. Combined with practical experience, the existing problems in the current measurement method of gas diffusion coefficient of coal were analyzed, at the same time, the direction and emphases of future research were prospected.