Under　environmental　excitation　and　based　on　observability,　an　online　model　to　predict　the　state　of　heavy-duty　machine　tool-foundation　systems　is　proposed　aimed　to　address　the　difficulties　of　directly　measuring　machine　tool　displacement　states.　The　aim　of　the　model　is　to　address　the　difficulties　associated　with　directly　measuring　machine　tool　displacements　in　real　time.　In　this　paper,　to　accurately　obtain　contact　parameters　of　the　joint　surface,　three　states-elasticity,　plasticity,　and　fracture-of　concrete　micro-bumps　were　studied.　To　obtain　the　equivalent　elastic　modulus　of　the　secondary　pouring　material　and　reinforced　concrete　material,　a　composite　foundation　constitutive　model　is　proposed　to　determine　the　equivalent　elastic　modulus　of　the　concrete　foundation.　Surface　topography　features　were　reconstructed　by　truncating　the　peaks　of　curves,　force　balance　relationships　were　defined　at　the　joint　surfaces,　and　a　metal-concrete　joint　contact　model　based　on　fractal　theory　was　deduced.　Based　on　the　joint　contact　model,　a　dynamic　model　of　the　heavy-duty　machine　tool-foundation　system　was　established.　The　dynamic　parameters　were　detected　in　real　time　and　used　to　reconstruct　the　above　dynamic　model　based　on　observation　theory.　Further,　an　estimation　model　was　established　to　describe　the　state　of　a　heavy-duty　machine　tool-foundation　system,　and　online　estimation　of　the　machine　tool　displacement　was　realized.　Finally,　the　estimation　model　was　validated　using　an　experimental　setup　of　the　heavy-duty　machine　tool-foundation　system　that　considers　joint　surface　factors.　In　conclusion,　the　model　provides　a　theoretical　basis　for　stable　online　control　of　heavy-duty　machine　tools.