With the promulgation of criminal law amendments, the retroactivity of the application of criminal law and criminal law amendments has attracted great attention in theory and practice. The retroactivity of criminal law involves the choice between the new crime and the old crime. According to the provisions of Article 12 of China's criminal law, if the punishment of the new crime is lighter than that of the original crime, the new crime shall apply. If the criminal law amendment is found guilty and the criminal law does not consider it a crime, it shall be declared innocent. The principle of strengthening the retroactivity of criminal law is conducive to the defendant, and the principle of non retroactivity is only applicable to the criminal law norms that are not conducive to the defendant. Among them, the application of the provisions on the crime of throwing objects at high altitude is an important window to observe the retroactive application between the criminal law and the amendment of the criminal law. Since the entry into force of the criminal law amendment (11), there have been many convictions and penalties for high-altitude throwing cases in China, and the convictions for high-altitude throwing include the acts that occurred before the entry into force of the criminal law amendment (11). Whether the criminal law amendment (11) has retroactive effect in the face of high-altitude parabolic behavior involves the comparison object of high-altitude parabolic crime. The retroactive application of criminal law means comparing different criminal law provisions and statutory punishment, and choosing the lightest punishment among two or more criminal law provisions. Therefore, the judicial officer must first consider the case at hand against the first legal provision in multiple criminal law provisions, and then think about the second, third or all other criminal law provisions to determine the criminal facts of the offender and punish the penalty. Among them, the comparison and choice between the new law and the old law are based on the principle of whether it is conducive to the defendant: first, according to the old law, it is a felony, while the new law is a misdemeanor, the new law is applicable; Second, according to the old law, it is a misdemeanor, while the new law is a felony, and according to the provisions of the new law, if there is no mistake in applying the old law to determine that this kind of behavior is a felony, the old law shall apply; Third, if the old law is a felony, but the new law is a misdemeanor, and according to the provisions of the new law, if the old law determines that such acts are felony errors, the new law cannot be applied for conviction and punishment, but acquittal. Of course, only by comprehensively comparing the criminal law and the criminal law amendment applicable to the specific penalty that the defendant should be sentenced in a specific case, can we draw a correct conclusion. The premise of the retroactivity of criminal law is the change of law rather than the change of facts. The law refers to the overall legal state on which the penalty depends, and the change of law refers to the change of laws and decrees sufficient to affect the scope of punishability and legal effect of behavior due to amendment or repeal. This change of law includes the change of penalty law The change of administrative regulations or orders to supplement the blank constituent elements (the change of filling norms) is only when the facts of the constituent elements are changed due to the amendment of laws and regulations, not the change of laws, such as the change of currency type and scope; Only when the legal opinion changes due to the change of law, it belongs to the change of law. If it only leads to the change of facts, it does not belong to the change of law if the disclosure provisions such as other methods are clarified or subdivided into other sub charges. If it leads to the change of the nature of facts, it belongs to the change of law if it is evaluated as a crime, not now evaluated as a crime, or it is evaluated as a crime a, and now evaluated as a crime B with completely different legal interests. The traditional view is that if the provisions of the criminal law are repealed after the implementation of the act and before the announcement of the judgment, the perpetrator should be declared innocent, because in this case, the law with the lightest punishment is no longer the law. The significance of this rule is that it properly expresses the protection of the perpetrator, does not require the arrangement according to the penalty at the time of the act, and the legal evaluation existing at the time of judgment should be the basis of criminal punishment. What is very controversial is that if a certain act is found to be a heavier punishment crime a according to the old law, it has been found by the new law that it does not belong to crime a, but to crime B, and crime a and crime B have completely different natures. In other words, according to the provisions of the new law, a certain behavior does not meet the constituent elements of charge A. at this time, can it be determined that it is not guilty according to the old law and that it is innocent by applying the old law? The author believes that this is a new problem brought about by the amendment of the criminal law. From the perspective of the provisions of the amendment itself, the qualitative nature of the behavior before the amendment is amended. When it is determined to be an act according to law, it is innocent. There is no doubt that if the high-altitude throwing is recognized as the type of behavior contained in the crime of endangering public safety by dangerous methods, there is no doubt that the high-altitude throwing that occurred before the criminal law amendment (11) is determined as the crime of high-altitude throwing according to the principle of "old and lighter". On the contrary, if high-altitude throwing is not the type of behavior covered by the crime of endangering public security by dangerous methods, does not constitute the crime of endangering public security by dangerous methods, and belongs to the behavior not prohibited by the criminal law, it should be acquitted according to the criminal law. At this time, the high-altitude throwing behavior that occurred before the amendment (11) of the criminal law shall be convicted of high-altitude throwing according to the principle of "old and lighter", It violates the principle of retroactivity of criminal law. If the two laws contain the same types of acts, but the former and latter laws have different qualitative and different legal effects, the problem of retroactivity will naturally occur. However, before and after the law, the characterization of this act must be accurate, otherwise it will also bring a wrong understanding of the application of the principle of retroactivity of criminal law. (outlook new era)