Direct current (DC) cable is the main current-carrying component in the DC transmission system. Its operating state is important to the stability of the metro traction power supply system. Once a fault occurs, it will not be able to supply power to the train normally and cause serious consequences. At the same time, its risk mechanism and propagation chain are complex, so it is not easy to analyze. Aiming at such characteristics, this paper proposes a dynamic risk analysis and evaluation method for metro power supply system based on fuzzy reasoning. In this paper, the risk propagation chain model of the subway DC power supply system causing the power supply system to stop power supply is studied, and the fault mechanism of DC cable breakdown is analyzed. The fuzzy probability is used to derive the risk propagation probability, and the graph theory is used to analyze the severity of the risk consequences caused by DC cable breakdown. Finally, a dynamic risk analysis and evaluation method for the DC cable breakdown risk propagation chain of the subway power supply system is established.