Abstract: The ladder method of three-level exclusion confirmed by understanding possibility, predicting possibility and the refinement of judicature is the method to judge whether crime of major flight accident complies with the principle of clarity. The lack of understanding possibility and predicting possibility makes the judgment method of “major flight accident” a problem for the theoretical and practical circles of criminal law in China. On the basis of Kelsen's positive law school, we should explain the “major flight accident” level by layer in accordance with the order of standardization, punishment and constitution. “Major flight accident” should be interpreted as “50 million yuan or more direct economic loss” as an objective result element, and “causing serious consequences” should be interpreted as “serious injury of 50 people or more” as an internal objective punishment condition.