Mt. Alishan is one of the most wellknown mountain forest railway, but the railway communication between Sta. 60k+550~61k+450 of Erwanping section has being disrupted until now, due to the serious run off of roadbase induced by the tremendous landcollapse, which occurred during the Typhoon Morakot since 2009. For early traffic reopen and capable of sustainable management of forest railway, the more expensive and long duration construction method Bypass Tunneling has been adopted for its rehabilitation. Owing to the lack of any available connections, the high construction difficulty of access roads should be built first for the mobilization and subsequent supplying of construction materials , equipments and manpower etc., and also for the access roads maintenance and workers evacuation when subjected to the uninterrupted rockfall and debris flow during the typhoon and rainstorm season. In addition to the construction characteristics and technical problems in the narrow hinterland of tunnel entrances, difficulty in tunnel entrancing through colluvial deposits and ecology protection for forest area, the original countermeasues of planning and design are inadequate. Finally, the tunnel is cut through with an effort after the several emergency treatments executed under the negotiation between the owner, supervisor and construction teams, and hope that the construction experiences of the project be useful for the references to similar cases in application.