A　method　for　fast　measuring　and　identify　the　six　geometric　errors　of　each　rotary　axes　in　Four-　axis　machining　center　was　invented.　The　method　adopted　the　ball-bar　to　measure　the　X,　Y,　Z　direction　deviations　of　the　centre　block　installed　on　the　rotary　table　in　the　different　rotation　angle.　And　deduced　the　geometric　error　identification　model　in　rotary　axes　based　homogeneous　transformation,　and　then　identify　the　axis　of　the　six　basic　geometric　errors.　in　order　to　reduce　the　influence　of　the　inaccuracy　of　the　ball-bar　and　the　reference　point　position,　this　paper　put　forward　new　method　based　on　the　analysis　of　the　sensitivity　matrix　method,　used　to　guide　rational　distribution　points,　so　as　to　improve　the　error　identification　accuracy.