<p>The chemical industry occupies a critical position in the national economy, but its complex production process leads to many risks in the chemical process system. From the system theory perspective, this study proposes a risk analysis method that integrates Systematic-Theoretical Process Analysis (STPA) and improved decision-making test and evaluation laboratory interpretation structural model (DEMATEL-ISM) for chemical process systems. First, the potential risk factors of the system are comprehensively identified by STPA, including the risks of equipment failure, operation error and element interaction anomaly; Then, the interactions of the risk factors are quantitatively analyzed by the improved DEMATEL-ISM method. By introducing the Maximum Mean Entropy Decrease (MMDE) algorithm, which constructs the hierarchical structure of the risk factors, revealing the critical risk points and the transmission paths. The results show that the temperature sensor failure and control algorithm error are the critical cause factors. Moreover, the actuator failure is the critical result factor, and the risk transfer path matches the actual operation logic of the system. This methodology is applied and validated through a case study of a typical ammonia synthesis process system. The study provides a scientific risk identification and analysis tool for safety management in high-hazard chemical process industries, such as petrochemicals and fertilizer production. Its application can assist enterprises and regulators in prioritizing safety investments, preventing major accidents, and minimizing associated production losses, environmental damage, and societal costs, thereby promoting sustainable economic development.</p>