Heavy　duty　machine　tool　has　some　special　points,　such　as　large　size,　complex　structure,　long　cycle　at　Installation　and　commissioning,　high　requirements　assembly　processes　and　so　on.　Therefore,　this　paper　established　a　mathematical　model　to　transform　the　origin　parts　of　the　gantry　machining　center　into　assembly　special　form　and　creates　a　software　as　a　plug-in　for　Solidworks　based　on　it,　proposes　an　easy　but　very　practical　assembly　method　based　on　Multi-body　system　under　virtual　environment.　This　method　can　calculate　assembly　deviation　caused　by　manufacturing　tolerance　very　quickly,　and　bring　the　sensitivity　information　clearly.　Assembly　deviation　sensitivity　and　assembly　method　proposed　in　this　paper　can　provide　a　way　for　the　virtual　assembly　of　heavy-duty　CNC　machine　tools,　Thus　provide　an　important　theoretical　basis　to　improve　the　performance　of　the　machine