In order to clarify the causes of hazardous chemical poisoning and suffocation accidents, the“2-4”model of behavioral safety theory was used to analyze the causes of 39 large and above hazardous chemical poisoning and suffocation accidents in chemical industry. The results show that the model can effectively trace the causes of accidents at the organizational and individual levels, and formulate targeted measures for accident prevention. The main reasons for hazardous chemical poisoning and suffocation accidents at the organizational level include insufficient management safety concepts and the lack of safety culture, which leads to deficiencies in the company's safety management system. The main reasons at the personal level are mainly due to inadequate safety education and training, insufficient safety knowledge of employees, weak safety awareness and poor work safety habits. Employees' habitual violation of process discipline and operating procedures is also one of possible reasons for the accident. When special operations are carried out in confined spaces,accidents are more likely to occur. Improper rescue may lead to the expansion of the accident.