The　stiffness　and　damping　of　mechanical　joint　are　modeled　by　the　zero　thickness　joint　interfaces　theory.　The　method　is　applied　to　analyze　the　dynamic　characteristic　of　the　gantry　frame　in　a　five　axis　turning-milling　compound　CNC　machine　tool.　The　model　test　is　carried　out　in　the　gantry　frame,　and　the　maximum　error　of　the　first　sixth　mode　is　5.63%.　The　experimental　and　analysis　result　show　the　zeros　thickness　joint　element　can　provide　an　effective　method　to　model　the　machine　joint　and　predict　the　dynamic　characteristic　of　the　assembled　structure.