Process safety analysis and loss control play imperative roles in chemical process industries. However, the lack of a systemic methodology for inherent safety studies in an unsteady state causes more hazards and accidents, which also prevent most industries from realizing inherent safety to its full extent. Here describes a method for analyzing the inherent safety of chemical processes in the unsteady state. As a quantitative description of the inherent safe level for a chemical process, the inherent safety degree (ISD) is defined appropriately. A model for ISD simulation is constructed to analyze a quantitatively inherent safety level of a chemical process by fuzzy logic. In this study, the difluoro-chloromethane (F22) pyrolysis process, one step of the tetrafluoroethylene (TFE) production process, was evaluated to validate the proposed method. In addition, sixteen technological nodes in four technological sections were compartmentalized according to their technical features and the inherent safety concept. Afterwards, an index set was established to assess the hazards of chemical substances, processes, and equipment based on the identification of risk factors and the inherent safety concept. Typically, the condensation dehydration node was proposed as a case study to explain the ISD calculation under unsteady state, and the time-course profile of the ISD was also obtained. The proposed method aims to judge ISD of a process under the unsteady state and provide detailed information for the chemical processes design.