Abstract: Article 20 of China’s Criminal Law makes public interest the object of protection in defence, which is a proposition with Chinese characteristics that is different from German and Japanese criminal law. Since environmental crimes are crimes against public interest, there is room for the evaluation of defence in environmental mass incidents. In the case of environmental pollution, for example, in the cause of defence, the violation of state regulations against the legal interests of the environment is the premise of defence. In the time of defence, the perpetrator must intentionally proceed to commit the act of crime as a benchmark for defence, with the continued plan of pollution and the absence of public mediation as a continuous feature of illegitimate infringement. As for the object of defence, the object can be a natural person or something that carries out pollution, and whether a corporate is a defence target is not a real issue. In terms of the limits of defence, it can only be done at the expense of the perpetrator’s right to freedom, reputation and property, and the resulting extra damage is excessive defense; if the goal is to harm the right to life and health of the perpetrator, it is an invasion other than defense, and the defender should be convicted additionally.