Urban　rail　transit　has　become　one　of　the　main　modes　of　people＇s　travel.　Once　an　accident　happens　in　the　urban　rail　system,　it　will　reduce　the　traffic　efficiency　and　affect　people＇s　normal　life.　Therefore,　it　is　very　necessary　to　evaluate　the　safety　risks　faced　by　the　system　during　its　operation　and　put　forward　effective　safety　management　measures.　In　this　paper,　a　safety　risk　assessment　method　combining　PCA-ISM-　Bayesian　network　is　proposed.　Firstly,　61　risk　indexes　are　extracted　from　the　collected　Beijing　subway　accident　data　by　combining　with　“subway　operation　safety　evaluation　standard”,　and　the　index　system　is　constructed　by　PCA　method.　Secondly,　use　the　ISM　model　to　analyze　the　logical　relationship　and　build　a　hierarchical　structure　among　indexes.　Finally,　the　Bayesian　network　is　embedded　to　build　a　security　risk　evaluation　model　to　evaluate　the　internal　risk　of　the　system.　The　result　shows　that　the　safety　degree　of　Beijing　subway　is　acceptable.　©　2024,　Beijing　Paike　Culture　Commu.　Co.,　Ltd.