Although　machine　tool　can　meet　the　specifications　while　it　is　new,　after　a　long　period　of　cutting　operations,　the　abrasion　of　contact　surfaces　and　deformation　of　structures　will　degrade　the　accuracy　of　machine　tool　due　to　the　increase　of　the　geometric　errors　in　six　freedoms.　Therefore,　how　to　maintain　its　accuracy　for　quality　control　of　products　is　of　crucial　importance　to　machine　tool.　In　this　paper,　machining　accuracy　reliability　is　defined　as　the　ability　to　perform　its　specified　machining　accuracy　under　the　stated　conditions　for　a　given　period　of　time,　and　a　new　method　to　analyze　the　sensitivity　of　geometric　errors　to　the　machining　accuracy　reliability　is　proposed.　By　applying　Multi-body　system　theory,　a　comprehensive　volumetric　model　explains　how　individual　geometric　errors　affect　the　machining　accuracy　(the　coupling　relationship)　was　established.　Based　on　Monte　Carlo　mathematic　simulation　method,　the　models　of　the　machining　accuracy　reliability　and　sensitivity　analysis　of　machine　tools　were　developed.　By　taking　the　machining　accuracy　reliability　as　a　measure　of　the　ability　of　machine　tool　and　reliability　sensitivity　as　a　reference　of　optimizing　the　basic　parameters　of　machine　tools,　an　illustrative　example　of　a　three-axis　machine　tool　was　selected　to　demonstrate　the　effectiveness　of　the　proposed　method.