The　modern　distribution　system　with　proliferated　distributed　energy　resources　(DERs)　integration　and　increased　demand　response　capacities　is　expecting　to　experience　a　deregulation　process　just　as　what　is　happening　in　the　transmission　system.　Ex-post　real-time　distribution　system　locational　marginal　pricing　(DLMP)　is　proposed　in　this　paper　as　an　effective　economic　signal　to　reflect　the　marginal　cost　of　supplying　incremental　loads　in　different　connecting　points　of　the　distribution　system　while　considering　actual　real-time　behaviors　of　DERs　and　residential　consumers.　DLMP　is　defined　for　each　phase　at　each　bus.　An　incremental　linear　optimization　problem　is　built　by　linearizing　nodal　current　injection-based　system　state　equations　at　the　current　system　operation　point,　which　is　provided　by　the　distribution　system　state　estimator.　The　objective　of　the　incremental　linear　optimization　problem　is　to　maximize　the　incremental　distribution　system　social　welfare,　while　constrained　by　a　set　of　incremental　system　state　equations,　power　balance　equations,　and　adjustment　limits　of　flexible　generations/loads.　Ex-post　real-time　DLMPs　are　calculated　via　the　optimal　dual　solutions　of　the　incremental　linear　optimization　problem.　A　modified　IEEE　13-bus　distribution　system　is　adopted　to　evaluate　the　performance　of　the　proposed　model.