In order to solve the problem of quantitative analysis of aviation unsafe events under uncertain conditions, based on the random and fuzzy theory, a mixed uncertain description of the subjective and objective variables that affect flight safety was proposed. To describe the subjective variables which were hard to be expressed by probability, the random variables that follow a uniform distribution in the λ-cut set of membership were introduced. Then, an aviation safety index and a numerical computational method under mixed uncertain conditions were proposed, which can reflect the aviation safety level concisely, intuitively and accurately. Through the Bow-tie model which is commonly used in the field of aviation safety, the relationship of the safety index and the membership of tire burst accident was obtained by simulation analysis. The quantitative results show that the aviation safety indices can be significantly improved with proper control of the membership degree.