By　the　experimental　modal　testing　to　the　main　structure　of　the　high-speed　horizontal　machining　center,　the　modal　parameters　such　as　the　natural　frequency,　damping　ratio,　stiffness　and　mode　shapes　are　obtained.　By　analyzing　the　vibration　characteristics,　the　critical　components　of　the　machining　center　is　at　the　spindle　front　bearing　part　and　the　vertical　column　on　which　the　screw　driving　spindle　box　to　move　in　vertical　direction　is　mounted　are　determined,　and　provide　an　important　basis　of　optimizing　the　structure　for　the　machining　center.　And　the　amplitude-frequency　characteristic　curves　of　the　critical　components　evaluate　the　dynamic　stiffness　as　the　key　indicators　to　provide　reliable　data　for　improving　processing　accuracy　and　cutting　ability　of　machining　center.