Abstract: To solve the problem of monitoring the evolvement of system safety risk state, this paper puts up a monitoring method of safety risk based on critical state and crucial component.First, the system's function, configuration and safety risk that the system encounters when working are analyzed.Based on the accident mechanism analysis, the system's safety risk state is identified.Then, the identification and calculating algorithm of critical state and crucial component are brought up.According to the critical state and crucial components, the detailed process of safety risk monitoring is present.Finally, the safety monitoring of a chemical system is carried out as an example.Result shows that this method is effective.