As　a　newly　invented　parallel　kinematic　machine　(PKM),　Exechon　has　attracted　intensive　attention　from　both　academic　and　industrial　fields　due　to　its　conceptual　high　performance.　Nevertheless,　the　dynamic　behaviors　of　Exechon　PKM　have　not　been　thoroughly　investigated　because　of　its　structural　and　kinematic　complexities.　To　identify　the　dynamic　characteristics　of　Exechon　PKM,　an　elastodynamic　model　is　proposed　with　the　substructure　synthesis　technique　in　this　paper.　The　Exechon　PKM　is　divided　into　a　moving　platform　subsystem,　a　fixed　base　subsystem　and　three　limb　subsystems　according　to　its　structural　features.　Differential　equations　of　motion　for　the　limb　subsystem　are　derived　through　finite　element　(FE)　formulations　by　modeling　the　complex　limb　structure　as　a　spatial　beam　with　corresponding　geometric　cross　sections.　Meanwhile,　revolute,　universal,　and　spherical　joints　are　simplified　into　virtual　lumped　springs　associated　with　equivalent　stiffnesses　and　mass　at　their　geometric　centers.　Differential　equations　of　motion　for　the　moving　platform　are　derived　with　Newton＇s　second　law　after　treating　the　platform　as　a　rigid　body　due　to　its　comparatively　high　rigidity.　After　introducing　the　deformation　compatibility　conditions　between　the　platform　and　the　limbs,　governing　differential　equations　of　motion　for　Exechon　PKM　are　derived.　The　solution　to　characteristic　equations　leads　to　natural　frequencies　and　corresponding　modal　shapes　of　the　PKM　at　any　typical　configuration.　In　order　to　predict　the　dynamic　behaviors　in　a　quick　manner,　an　algorithm　is　proposed　to　numerically　compute　the　distributions　of　natural　frequencies　throughout　the　workspace.　Simulation　results　reveal　that　the　lower　natural　frequencies　are　strongly　position-dependent　and　distributed　axial-symmetrically　due　to　the　structure　symmetry　of　the　limbs.　At　the　last　stage,　a　parametric　analysis　is　carried　out　to　identify　the　effects　of　structural,　dimensional,　and　stiffness　parameters　on　the　system＇s　dynamic　characteristics　with　the　purpose　of　providing　useful　information　for　optimal　design　and　performance　improvement　of　the　Exechon　PKM.　The　elastodynamic　modeling　methodology　and　dynamic　analysis　procedure　can　be　well　extended　to　other　overconstrained　PKMs　with　minor　modifications.