A　flexible　dynamic　model　of　a　multi-axis　synchronous　gantry　machining　center　was　developed　with　a　finite　element　analysis　software　SAMCEF　Mecano.　The　dynamic　solution　was　obtained　with　implicit　Non　linear　method　and　HHT　recurrence　algorithm　based　on　modified　Newmark　algorithm.　The　position　error　and　velocity　were　analyzed.　The　influence　of　elastic　deformation　on　position　error　was　developed　contrast　between　flexible　body　and　rigid　body.　The　dynamic　model　was　proved　to　be　valid　by　the　comparison　of　the　results　between　simulation　and　theory.　It　shows　that　the　position　error　and　the　variation　of　velocities　are　related　to　the　vibration　characteristic,　driving　motor　and　nonlinear　characteristics　of　machining　center.　The　results　provide　necessary　information　for　analysis　of　dynamic　performance,　dynamic　optimization　design,　dynamic　simulation　of　machining　center.　The　research　on　the　machining　center　is　of　great　theoretical　significance　and　practical　value.　©　2010　IEEE.