Based　on　the　theory　of　multi-body　system　and　homogeneous　coordinate　transformation,　this　paper　analyses　the　error　of　five-axis　CNC　machine　tool　and　establishes　the　machining　precision　model　firstly.　Then　taking　the　five-axis　double　wall　CNC　machine　tools　as　an　example　and　according　to　the　structure　of　the　machine　and　the　assembly　relationship　of　key　parts,　the　geometric　errors　of　the　machine　tools　are　analyzed.　Meanwhile,　the　coordinate　systems　of　all　the　key　components　and　characteristic　matrix　among　the　bodies　are　established.　Finally,　the　Machining　Accuracy　Model　of　Machine　Tool　was　established.　It　lays　the　foundation　for　the　accuracy　of　subsequent　design　work.