Probability-based　seismic　fragility　analysis　provides　a　quantitative　evaluation　of　the　seismic　performance　exhibited　by　structures.　This　study　introduces　a　framework　to　perform　seismic　fragility　analysis　of　utility　tunnel　and　internal　pipeline　system　considering　wave　passage　effect　of　the　ground　motion　spatial　variation.　The　numerical　model　of　a　double-beam　system　resting　on　a　nonlinear　foundation　is　established　to　simulate　the　soiltunnel-pipeline　interactions.　17　pairs　of　earthquake　records　are　chosen　and　scaled　as　inputs　at　the　outcrop.　One-dimensional　(1D)　free-field　analyses　are　conducted　to　obtain　the　ground　motion　time　histories　at　the　bottom　slab　of　the　utility　tunnel,　and　then　incremental　dynamic　analysis　(IDA)　is　performed　for　the　utility　tunnel-internal　pipeline　system.　The　damage　states　(DSs)　are　defined　by　the　maximum　joint　opening　for　the　utility　tunnel　and　maximum　strain　for　the　internal　pipeline,　and　the　peak　bedrock　velocity　(PBV)　is　determined　to　be　the　most　representative　intensity　measure　(IM)　for　developing　the　seismic　fragility　curves.　The　seismic　fragility　curves　of　the　system　are　constructed　using　the　joint　probabilistic　seismic　demand　model　(JPSDM)　and　Monte　Carlo　sampling　method.　The　research　findings　indicate　that:　(1)　the　framework　proposed　in　this　study　is　suitable　for　the　fragility　assessment　of　long-extended　utility　tunnel-internal　pipeline　system;　(2)　the　utility　tunnel　and　internal　pipeline　as　a　system　exhibit　greater　fragility　compared　to　either　one　of　the　components,　and　the　JPSDM　and　Monte　Carlo　sampling　method　for　the　system　fragility　analysis　is　more　precise　than　the　first-order　bound　method;　(3)　the　proposed　fragility　curves　in　this　study　provide　quantitative　damage　probabilities　for　the　individual　components　and　system　under　different　seismic　intensity　levels.　(4)　The　IM　values　corresponding　to　50%　exceedance　failure　probability　of　the　whole　system　is　1%-3%　lager　than　that　of　the　upper　bounds,　and　it　is　3%　to　5%　less　than　that　of　the　lower　bounds.　The　conservative　upper　bound　is　a　more　suitable　approximation　for　system　fragility.　(5)　It　should　be　noted　that　the　obtained　fragility　curves　are　valid　for　the　considered　tunnel-pipeline　structure　and　site　conditions.　For　different　tunnel　structures　and　site　conditions,　the　fragility　curves　can　be　constructed　following　the　same　steps　outlined　in　this　study.