The traditional method of fuzzy comprehensive assessment has the problem that the evaluation result is not well-determined because the choosing of the membership function is too subjective.A qualitative and quantitative conceptual conversion model, named the cloud model, is introduced, and a fuzzy comprehensive assessment method based on the cloud model is proposed.First, by introducing the cloud model to replace the single membership function in the original fuzzy comprehensive assessment method, the randomness and ambiguity of the qualitative results are characterized.Secondly, in the evaluation process, the problem of absolute boundary is avoided by improving the division of the evaluation scope.At the same time, a new quantification interval is determined based on the cross quantification interval, and the cloud model is obtained accordingly to avoid the computing of the reverse cloud.Finally, the evaluation performance of the three methods of the cloud-model comprehensive evaluation method, the original fuzzy comprehensive evaluation method and the proposed algorithm is analyzed by evaluating the example of flight avoidance safety, and the validity of the proposed method is verified.