Being　an　important　engineering　in　transport　lifeline　system,　bridges　were　severely　damaged,　even　ruined,　in　many　earthquakes　with　moderate　intensity.　In　this　context,　the　study　of　the　structural　seismic　fragility　of　the　bridges　attracted　more　attention　and　developed　all　around　the　world.　Partially　cable-stayed　bridges　were　developed　rapidly　and　constructed　broadly　at　home　and　abroad　in　the　past　10　years,　due　to　successful　combination　of　economy　and　aesthetics.　However,　this　type　of　bridge　has　not　yet　been　tested　by　strong　earthquakes;　the　structural　seismic　fragility　of　the　brideges　in　a　possible　earthquake　is　still　unknown,　which　has　to　be　studied.　Based　on　the　existing　study　results　about　bridges,　the　seismic　fragility　of　the　partially　cable-stayed　bridge　with　single　tower　is　analyzed　under　the　cross-bridge　ground　motion.　Five　levels　of　damaged　limit　states　are　defined,　and　the　fragility　curves　of　piers,　towers　and　whole　bridge　are　established.　The　study　results　show　that　under　cross-bridge　ground　motion,　the　seismic　fragility　of　the　partially　cable-stayed　bridge　with　single　tower　is　mainly　controlled　by　medium　pier　and　buffers.