Seismic　intensity　measures　(IMs),　which　are　closely　related　to　both　earthquake　hazards　and　structural　responses,　play　a　critical　role　in　the　performance-based　earthquake　engineering　(PBEE)　framework.　This　paper　aims　to　investigate　and　define　the　most　representative　IMs　for　probabilistic　seismic　demand　model　(PSDM)　for　the　longitudinal　utility　tunnel　and　internal　pipeline　system.　Similar　to　the　requirements　by　the　Chinese　Code　for　seismic　design　of　urban　rail　transit　structures,　the　utility　tunnel　in　this　study　is　assumed　being　buried　in　four　typical　engineering　site　classes　for　the　analyses.　Soil-tunnel-pipeline　interactions　are　simulated　using　a　double-beam　system　resting　on　a　nonlinear　foundation.　Soil-tunnel　interaction,　tunnel-pipeline　interaction　and　joint　connections　are　modeled　as　nonlinear　springs　with　different　mechanical　properties.　A　series　of　17　pairs　of　outcrop　ground-motion　records　and　27　commonly　used　IMs　are　selected　in　the　analyses.　Engineering　demand　parameter　(EDP)　is　defined　based　on　the　maximum　joint　opening　and　the　maximum　strain　of　the　utility　tunnel　and　internal　pipeline,　respectively.　The　selected　IMs　for　predicting　the　seismic　responses　of　tunnel-pipeline　systems　are　tested　using　different　criteria,　i.e.,　correction,　efficiency,　practicality,　and　proficiency.　The　final　decision-making　procedure　employs　a　fuzzy　multi-criteria　decision　method.　The　numerical　results　indicate　that:　(1)　The　velocity-related　IMs　are　the　most　representative　IMs　based　on　the　four　criteria　for　structures　buried　in　four　sites　of　different　conditions;　(2)　The　optimal　seismic　IMs　vary　with　different　criteria,　site　classes　and　structure　types.　According　to　the　fuzzy　multi-criteria　decision　approach,　optimal　IMs　for　the　tunnel-pipeline　system　are　PGV,　PGV,　EPV　and　HI　for　site　classes　I　–　IV,　respectively.　The　proposed　optimal　IMs　can　be　utilized　to　construct　seismic　fragility　curves　of　utility　tunnel,　internal　pipeline　and　tunnel-pipeline　systems　in　four　different　site　classes.　©　2024　Elsevier　Ltd