Aiming　at　the　characteristics　of　gantry　machining　tool　such　as　large　size,　complex　structure,　high　requirements　assembly　processes　and　long　cycle　at　installation　and　commissioning,　a　predictive　optimization　method　for　assembly　scheme　was　proposed.　The　mathematical　model　based　on　multi-body　system　theory　was　established　to　translate　the　actual　assembly　process　into　transformation　form　with　multiplication　of　assembly　unit　status　description　matrix　and　assembly　unit　process　description　matrix.　The　theory　model　of　machining　tool　assembly　was　constructed,　and　the　predictive　method　for　assembly　scheme　was　given　by　analyzing　the　three　indicators　of　accuracy,　cycle　and　correlation　coefficient.　Multiple　target　area　was　used　to　reflect　the　optimization　effect.　The　special　software　was　developed　based　on　MATLAB　to　realize　transform　calculation　and　overlay　analysis　of　matrix　transform　between　modules,　which　could　provide　evidences　for　the　establishment　and　validation　of　gantry　machining　tool　assembly　method.