Abstract: Aiming at the security challenges faced by the Wireless Transmission Device System for EMU/DMU (WTDS), this paper proposed a security risk assessment method based on Bayesian attack graphs. The paper constructed a Bayesian attack graph model targeting two key targets, including the vehicle-mounted data platform and the ground data center. It quantified the probabilities of atomic attack nodes from three dimensions of vulnerability value, attack cost, and attack benefit, and calculated the static and dynamic reachability probabilities of attribute nodes by combining the logical relationships between nodes. Simulation results show that the proposed method can quantitatively analyze the attack risks of adversaries targeting the vehicle-mounted data platform and ground data center of WTDS, and provides quantitative support for the security protection and emergency disposal of WTDS.