As　the　main　geometric　defect　in　pipeline　maintenance,　dent　has　been　paid　more　attention　by　pipeline　managers　because　of　its　strong　stress　concentration.　To　investigate　the　formation　mechanism　of　a　pipeline　dent,　an　indentation　test　of　a　pipe　subjected　to　concentrated　lateral　load　was　carried　out　in　the　laboratory　to　simulate　the　formation　process　of　the　dent,　and　a　3D　numerical　model　corresponding　to　the　test　was　established　to　verify　the　results　between　the　experiment　and　simulation.　Subsequently,　the　stress　and　strain　response　of　the　dented　pipeline　was　analyzed　in　detail　in　various　stages　of　dent　formation　process.　Deformation　analysis　revealed　that　the　residual　stresses　state　formed　in　the　dented　area　after　unloading　is　related　to　the　depth　of　the　dent,　which　may　be　in　tension　or　in　compression.　During　the　formation　of　the　dent,　the　pipeline　presents　＂similar　to＂-type　wave-like　bending　state　in　the　axial　direction.　These　dent　formation　mechanisms　may　provide　a　guidance　for　dent　assessment　studies.