Abstract: It is more difficult to measure a fine-pitch gear than a medium pitch gear because of the effect of geometrical dimension and mechanical performance.With technical development,the dimension of a fine- pitch gear is getting smaller and smaller but the precision is becoming higher and higher,especially due to Mi- cro-gear's appearance.It leads to a new challenge to measure a fine-pitch gear.Adopting traditional measure- ment methods,the analytic measurement for gears can not reach 0.2 mm and the functional measurement for gears can not reach 0.1 mm.Owing to the strict limitations of gear diameter,gear single-flank rolling test can not attract the attention which they should be deserved.It can be said that the traditional measurement meth- ods have been unable to meet small modulus gear measurement requirements.So the technology of fine pitch gear measurement has become a hot research in recent years.Currently,the technology of fine-pitch gear measurement shows new development trends,such as the gear parallel measuring technology based on the op- tics;the gear analytic measuring technology based on the optical fiber probe and gear single flank roiling test.