The construction of Karst tunnel is affected by such factors as rock mass quality, groundwater and excavation method. In order to study the risk of tunnel construction in karst area, the influencing factors are divided into three categories and ten factors, and a two-level comprehensive evaluation model is established based on analytic hierarchy process and fuzzy mathematics. By selecting the membership function of trapezoidal distribution, the membership degree of various factors in different risk levels is determined. Taking a super-long tunnel in Sichuan Province as an example, the construction risk of the project is calculated and analyzed, and compared with the results of advanced prediction. It is found that the evaluation results are consistent, which shows that the evaluation results can provide a certain basis for construction operations.