Fragility　analysis　is　widely　used　in　seismic　performance　assessment　of　bridges　but　uncertainties　in　seismic　demand　and　bridge　modelling　affect　the　accuracy　of　assessment　results.　This　study　proposes　a　digital　twin-based　collapse　fragility　assessment　method　for　long-span　cable-stayed　bridges　under　strong　earthquakes.　A　scaled　long-span　cable-stayed　bridge　and　its　shake　table　tests　are　taken　as　an　example.　Three　finite　element　(FE)　models　of　the　bridge,　including　a　design　document-based　FE　model,　a　linearly　updated　FE　model,　and　a　nonlinearly　updated　FE　model,　are　established　to　demonstrate　the　necessity　of　the　digital　twin-based　assessment.　Incremental　dynamic　analyses　(IDA)　are　conducted　to　calculate　the　collapse　fragility　curves　of　the　FE　models.　The　assessment　results　are　compared　with　the　test　results　in　terms　of　collapse　mechanisms,　collapse　ground　motion　intensities,　and　collapse　probabilities.　It　is　found　that　the　proposed　method　is　feasible　and　accurate　for　seismic　collapse　assessment　of　long-span　cable-stayed　bridges.