The　interface　crack　is　the　typical　defect　in　fracture　mechanics,　and　it　often　exists　inside　the　layered　composite　rocks　(LCRs).　How　does　it　respond　to　the　stress　circumstances　with　a　large　anisotropy?　Is　of　paramount　importance　in　the　stability　evaluation　of　underground　engineering.　This　issue　is　addressed　in　this　study　where　the　true　triaxial　tests　with　the　loading　rate　of　0.05 mm/min　are　conducted　on　the　two-layered　sandstone-granite　composite　structures　containing　the　interface　cracks.　Sandstone　and　granite　have　a　strength　of　92.1　and　135.4 MPa,　respectively.　Results　show　that　the　interface　crack　significantly　weakens　the　LCR　strength　under　true　triaxial　stress.　The　interface　crack　tips,　as　typical　stress　concentrator,　are　revealed　as　the　main　sources　of　fracture　initiation　and　propagation,　and　the　interface　crack　tips　are　also　found　as　an　essential　joint　for　the　fracture　containment　within　the　weaker　layer.　The　fracture　cluster　is　formed　ahead　of　the　interface　crack　tip　where　tensile　fracture　co-exists　with　shear　fracture.　Moreover,　the　macro-failure　initiation　mode　exhibits　the　interface　crack　tip　fracture　in　the　quasi-3D　failure　manner.　Main　failure　planes　of　LCRs　appear　sub-orthogonally　to　σ3　and　display　the　mode　of　σ3-transverse-symmetric　fracturing.　Finally,　the　coupling　mechanisms　among　the　interface　crack,　the　stress　anisotropy　and　the　mechanical　contrast　between　the　layers　are　revealed.　©　The　Author(s),　under　exclusive　licence　to　Springer　Nature　Switzerland　AG　2023.