Abstract: A new assessment method combined catastrophe theory and fuzzy mathematics is established and applied for the first time to evaluate and select the optimum project of the underground gas storage, in which subordinate functions of assessment indexes are derived with the combination of catastrophe theory and fuzzy mathematics. Based on these subordinate functions, comprehensive values of all candidate underground gas storage projects are calculated, on which we base to select the best project. From example testing, it shows that result evaluated by the method is in accordance with other evaluation method’s very well. The method can ensure the veracity and creditability of the evaluated result and avoid the randomicity and troubling of hierarchy process, factor analysis, fuzzy comprehensive appraisal and other assessment methods.