To further explore the uncertainty and fuzziness in the analysis and evaluation of water and mud inrush disaster in karst tunnel, a novel hazard assessment model for water and mud inrush disaster in karst tunnel is established based on interval number theory, fuzzy comprehensive evaluation method, and analytic hierarchy process. The primary factors affecting water and mud inrush, including formation lithology, geological structure, geological conditions, topographic and geomorphic, positional relationship between tunnel and groundwater, and the circulation and migration conditions of groundwater, are analyzed, and an evaluation system containing six primary indices and 13 secondary indices is constructed to unify the certainty and uncertainty of the evaluation index of water and mud inrush in karst tunnel in the form of interval. This provides a more practical solution for disaster prevention and overall evaluation of tunnel water and mud inrush interval in karst area. The typical cases and application results show that the risk level of water and muck inrush in karst tunnel assessed by the model is consistent with that revealed by the case, validating the rationality and practicability of the proposed method and the calculated risk level.