It　is　inevitable　that　the　mechanical　part　has　error　when　machining.　To　increasing　the　machining　precision　and　decreasing　the　shape　and　position　error,　error　compensation　is　one　way.　The　geometry　error　parameter　is　necessary　when　the　error　compensation　model　is　founded　and　the　compensation　data　is　calculated.　The　common　measuring　and　identifying　methods　are　introduced　in　this　article.　Their　mathematic　models　and　solutions　are　listed　and　their　merits　and　drawbacks　are　compared.　This　method　has　been　applied　in　CNC　error　compensation　and　the　effect　is　advisable.　©　(2014)　Trans　Tech　Publications,　Switzerland.