This　study　incorporates　the　concept　of　deflection　curves　with　displacement　influence　lines　in　order　to　propose　a　new　concept　of　quasi-static　deflection　surface　for　short-to-medium　span　bridges　under　moving　loads.　Analytical　formulas　of　deflection　surfaces　are　derived　using　the　principle　of　virtual　work.　An　alternative　form　by　deflection　matrix　is　given　for　practical　applications.　After　that,　the　deflection　surface　difference　of　a　simply　sup-ported　beam,　as　well　as　a　continuous　box-girder　bridge　before　and　after　damage,　was　used　to　locate　damage.　Lastly,　the　superstructure　model　of　a　continuous　box　girder　bridge　with　variable　cross　sections　was　statically　tested　in　the　laboratory.　Measured　deflections　were　used　to　construct　the　deflection　surfaces　of　the　box　girder　bridge　model　before　and　after　damage.　The　artificial　damage　was　successfully　located　using　the　difference　of　these　deflection　surfaces.　The　analysis　results　demonstrate　that　the　proposed　method　is　also　applicable　to　box　girders　with　variable　sections.　Damage　localization　can　be　achieved　using　structural　measured　deflection　data　be-fore　and　after　damage.　The　peaks　on　a　deflection　difference　surface　correspond　to　the　damage　locations,　and　the　peak　magnitudes　reflect　the　changes　in　damage　severity　to　some　extent.　©　2022,　Editorial　Department　of　JVMD.　All　right　reserved.