The　supportfree　printing　of　overhanging　structure　arouses　enormous　interest　for　its　advantages　to　eliminate　the　need　for　support　removal　and　to　improve　the　efficiency　in　laser　powder　bed　fusion　(L-PBF)　additive　manufacturing.　However,　the　improvement　of　down　-facing　surface　quality　remains　a　significant　challenge,　where　an　in-depth　understanding　of　the　formation　of　overhanging　tracks　is　essential.　This　paper　developed　a　multiphysics　model　of　overhanging　tracks　in　L-PBF　to　systematically　investigate　the　formation　mechanisms　of　key　features　such　as　discontinuity　and　dross,　as　well　as　their　correlation　with　surface　roughness.　It　reveals　that　there　are　two　main　causes　of　discontinuity　of　overhanging　tracks:　the　coalescence　and　balling　of　the　melt　under　low　energy　density,　and　the　irregular　sinking　of　melt　pool　at　the　overhanging　edge.　The　high　energy　density　could　mitigate　the　occurrence　of　discontinuous　tracks,　but　it　might　also　lead　to　undesirable　dross　upon　the　complete　penetration　of　the　overhanging　structure.　The　relationship　between　processing　parameters,　morphological　defects　and　surface　roughness　were　systematically　discussed,　which　revealed　the　necessity　to　tailor　processing　parameters　for　different　overhang　angles　to　improve　the　down　-facing　surface　quality.　Furthermore,　the　significant　correlation　between　the　single-track　morphology　and　the　down　-facing　surface　roughness　has　been　demonstrated　quantitatively,　which　proposed　a　practical　way　to　predict　the　trend　of　the　down　-facing　surface　quality　by　single-track　simulation.　This　could　help　improve　the　supportfree　printing　process　in　metal　additive　manufacturing.