Abstract：Research purposes： Because of the characteristics of argillization induced by water, the widespread Xigeda strata in the Southwestern areas severely impact the tunnel engineering construction along the Chengdu-Kunming  Railway. Thus, it is of significance to carry out the study on Xigeda strata tunnel. We made field research on the catastrophe pattern of Xigeda strata tunnel, deeply studied the catastrophe feature and mechanism of the tunnel surrounding rock in Xigeda strata by means of field sampling, indoor test, numerical modeling, field monitoring, theoretical analysis and the like.  Research conclusions：（1）When the tunnel crosses the Xigeda strata, catastrophes appear, for example, the large sedimentation of vault, big horizontal convergence, the hunching and mud burst of the inverted arch, and the collapse of face and other typical catastrophe patterns.（2）When water content ranges within 0% and 25%, the displacement changes  trends of the vault crown settlement, the horizontal convergence, the uplifting of the inverted arch, and the extracted deformation of face are basically the same. Moreover, with the gradual increase of water content during the excavation process, the deformation of the tunnel surrounding rock becomes clearer. Especially when water content gradually changes towards the value of 30% from that of 25%, the displacement changes of those parts increase sharply and when the water content reaches 30%, the accumulated sedimentation values of every part of the tunnel reach the tunnel catastrophe state. Thus, 25% of the water content can be marked as the critical value of the catastrophe of the Xigeda tunnel, while 30% of that is the catastrophe value. （3）We establish the judgment matrix and evaluate it through setting up the index system of catastrophe factor and then determine the weight of every factor by using the analytic hierarchy process. The catastrophe source factor that influences the weight most is the geology of Xigeda itself and the 〖JP2〗rock mass mechanics with the factor being 0.625 0, followed by the factor of hydrogeology, which is 0.238 5, groundwater index is the most important factor in hydrogeological factors. （4）The conclusions obtained can provide guidance  for the rapid and safe construction of Xigeda strata tunnel in the Southwestern Areas. 