Abstract: In order to improve evaluation accuracy of flight safety risk,grey system theory and comprehensive integration weight method are combined to develop a quantitative evaluation method considering uncertainties of factors affecting safety risk of flights.An index system is established from four aspects of crew,equipment,environment,and management.The weight of each index is determined by the comprehensive integrated weight method based on the principle of minimum entropy.A model is developed based on gray system theory,which is used to evaluate flight safety risk,and define the main indices which affect safety of flights.Rationality and feasibility,and effectiveness of this method are validated from a case study.The results show that the method can solve the problem of uncertainties in evaluation processes to the maximum extent.