In　view　of　the　limitations　of　traditional　research　tools　on　interfacial　failure　mechanisms　in　fiber/PPESK　composites,　this　work　proposes　a　multiscale　research　tool　to　carry　out　an　in-depth　study　of　the　interfacial　behavior　between　fibers　and　matrix.　Based　on　microdroplet　debonding　tests,　at　the　mesoscopic　scale,　the　influence　of　residual　thermal　stress　on　the　interface　damage　mode　is　explored　through　finite　element　(FEM)　simulations.　The　evolution　mechanism　of　composite　material　interfaces　in　spatial　and　temporal　dimensions　is　examined　based　on　changes　in　interfacial　stress　distribution,　energy　dissipation,　and　damage　morphology　during　the　debonding　process,　which　can　be　summarized　as　follows:　accompanied　by　elastic-plastic　deformation　and　friction　effects,　the　progressive　process　from　localized　to　complete　failure　presents　a　dominant　Type　II　damage　mode　at　the　interface.　To　further　explore　the　interface　failure　mechanism　at　the　molecular　level,　an　interface　model　of　CF/PPESK　composite　materials　was　established　using　molecular　dynamics　(MD)　method.　By　monitoring　the　atom　movement　trend,　the　＇fiber-matrix　displacement　synergistic　effect＇　in　the　interfacial　shear　damage　process　was　revealed,　thereby　establishing　a　multiscale　mapping　relationship　of　composite　material　interface.　Based　on　this,　the　combination　of　FEM　and　MD　was　utilized　to　investigate　the　interface　damage　process　of　composite　materials　under　different　service　conditions　and　to　reasonably　predict　the　initiation　and　expansion　of　microcracks.　This　study　provides　a　pioneering　perspective　on　interface　damage　research　in　composite　materials　with　a　＇top-down＇　multiscale　approach.　©　2024　Elsevier　Ltd