Large　gears　are　the　indispensable　parts　of　large-scale　equipments,　but　it　is　a　tough　task　to　inspect　large　gears　owing　to　their　increasing　technical　specifications,　large　size　and　heavy　weight.　Many　factors　affecting　large　gears　measurement　are　analyzed.　The　measuring　principals,　methods　and　typical　instruments　of　two　kinds　of　large　gears　measurement:　off-machine　measurement　and　on-machine　measurement,　are　reviewed　in　detail,　as　well　as　their　specific　advantages　and　disadvantages　are　discussed.　Based　on　the　analysis　of　manufacture　characters　and　application　requirements　for　large　gears,　the　general　requirements　and　development　direction　are　summarized,　that　are　holistic　model　description　and　fast　measurement.　The　new　ideas,　principles,　solutions　and　artifact　are　introduced　as　well,　especially,　to　inspect　large　gears　with　small　instruments　effectively　will　become　a　trend.　As　a　solution,　a　new　on-machine　measuring　method　combining　the　virtues　of　laser　tracking　with　coordinate　metrology　can　figure　out　the　problem　of　establishing　relationship　between　the　measuring　instrument　and　large　gear,　this　method　also　can　be　applied　to　the　inspection　of　others　complex　and　large　parts,　so　it　shows　a　favorable　application　prospect.　©　2013　Journal　of　Mechanical　Engineering.