Due to some reasons such as geology and complex environment, the railway tunnels built in the mountain area always have a long construction period and construction risks. Some accidents such as collapses are prone to happening during tunnel construction. Hence, the judgment matrix, weight and membership degree of influencing factors on collapses of Dengjiawan Tunnel on ChengduKunming Railway are determined by comprehensive fuzzy hierarchy analysis method; an accident consequence assessment model is established by risk consequenceequivalent estimation method; and by combining these two methods, a model which can be used to assess the probability of an accident is established. The hazard level of this model is particularly classified according to the relevant railway management regulations and provisions of risk assessment. It is concluded that a new assessment method combined with the comprehensive fuzz analysis method and the consequenceequivalent estimation method is obtained, and the assessment results are in good agreement with the actual tunnel excavation conditions, which can effectively apply to mountain railway tunnels.