If applicable, it has retrospective effect; If not applicable, there is no traceability. At present, the principle of "from the old to the light" is generally adopted in criminal laws in various countries, that is, the new law does not go back in principle, but if the new law does not consider crimes or the punishment is light, the new law will apply. The retroactivity of the civil law, after the promulgation and implementation of the new civil law, is also applicable to civil relations that occurred before its entry into force but were not judged according to judicial procedures. There are strong and weak points, and the civil relations and facts arising before the implementation of the new law can only be applied from the date of implementation, which is weak retroactivity; However, if the civil relations and facts are traced back to the time when the relevant provisions of the new law are applicable, it belongs to the intensity retroactivity. Only by making the law public can members of society be required to abide by it and be binding. If we want to change the legal relationship established by the old law with the new law, it will inevitably affect the stability of social order. Therefore, civil law generally only applies to the facts and relationships that occur after the entry into force. "The law should not be retroactive" is a principle established as early as Roman law and recognized by later generations. China's civil law also adopts the principle that civil law norms are generally not retroactive. However, while confirming in principle that civil law has no retroactivity, it does not rule out that the state can make some retroactivity provisions under certain circumstances according to objective needs. For example, on 1 October 20th, the Measures for Handling Debt Disputes in New Areas promulgated by the former Government Council and other articles 1950, 10, etc.1stipulated that "all debts owed to landlords by farmers and other working people before liberation shall be abolished". The retroactivity of civil law must be clearly stipulated by national laws or interpreted by organs with the right to interpret laws. According to the principle of non-retroactivity, such legal provisions or interpretations are exceptions.