Two-layer theory. According to official website of Hunan Normal University Law School, in the criminal law class of graduate students of Hunan Normal University Law School, teachers usually explain criminal law from the perspective of two classes. The theory of two courses refers to the constitutive elements of due, illegal and responsibility, while the theory of four elements refers to the object, objectivity, subject and subjective aspects of crime, so the criminal law of graduate students in Hunan Normal University Law School is applicable to the two courses.