Abstract: In the absence of relevant legislation, it is necessary to establish a hierarchical approach to cases involving illegality cognition. In the case of defense of "mistake of illegality cognition" raised by the perpetrator, it is necessary to take a step-by-step approach of "fact judgment-normative judgment-hierarchical and detailed judgment". Firstly, the subjective and objective facts of the case should be comprehensively analyzed using deductive reasoning to confirm whether there is illegality cognition. If it can be confirmed, it should be directly determined as an invalid defense. In cases where there is a mistake, the mistake of illegality cognition can be used as a discretionary sentencing circumstance and a reason for exoneration in special circumstances. When there is no possibility of illegality cognition, it should be recognized as an incident of innocence, and the judge can exonerate by invoking the provision of unforeseen events or anticipated impossibility, or by being loyal to the law. Finally, when determining the possibility of illegality cognition, it is necessary to distinguish between clear possibility and ambiguous possibility. When there is clear possibility, basic facts in criminal presumption can be used for judgment, while when there is ambiguous possibility, a detailed examination of the predictability of knowledge of the law, obstacles to knowledge of the law, and the basis for confirming the legality of the behavior is required.

Key words: mistake of illegality cognition, criminal inference, possibility of illegality cognition, criminal presumption, exoneration