The classification of railway gas tunnel has a significant influence on tunnel construction and operation. Firstly, the standards of classification and fortification of gas tunnel (mine) in relevant existing rules, codes and guidelines are analyzed and compared. And then, the problems of the classification of gas tunnel are summarized, triplephase classification method is established based on the collected data and working keys of planning phase, construction phase and operation phase, and the classification standards of every phase are put forward. Finally, the classification standards of fortification of gas tunnel is established based on environment classification standards of running gas tunnel; furthermore, the fortification structure system of gas tunnel can be established, so as to guarantee the construction and running safety of gas tunnel.