Tunnel is one of the most durable structures in all kinds of geological engineering structures, which often has one hundred years or more service life cycle. However, there are more and more cases about tunnel damage in recent years. In this paper, we used a case study of tunnel failure caused by upper slope instability in Central CrossIsland Highway in Taiwan to discuss the process of emergency treatment in disaster area. We did some largescale field geological investigation along the road to explore the relevance of the reasons which caused disaster and the engineering geological characteristics. Finally we made some brief description on the assessment of disasterprone area and the concept of disaster control that had been promoted recently in mountain highway in Taiwan.