Based　on　software　of　OpenSees,　three-dimensional　finite　element　model　of　typical　Lower-tower　Cable　Stayed　Bridge　is　established,　and　the　randomness　of　concrete　strength　as　well　as　steel　strength　is　taken　into　account　by　Latin　hypercube　sampling　method.　As　a　result,　bridge　structure-ground　motion　samples　are　produced.　Then　Incremental　Dynamic　Analysis　is　employed　in　transversal　and　longitudinal　direction　concerning　the　participation　of　vertical　ground　motion.　Finally,　steel　strain　of　main　towers　and　side　piers　as　well　as　concrete　strain,　stress　of　cables,　moment　of　main　beams　of　the　bridge　are　presented　as　seismic　response　of　structural　components.　Then,　earthquake　fragility　analysis　is　carried　out　coupled　with　corresponding　damage　index.　Vulnerability　curve　fitting　are　made　by　choosing　a　reasonable　distribution　function　and　its　parameters.　The　study　provides　a　reference　for　seismic　design　and　seismic　risk　assessment　of　the　similar　bridge.