Involute prototype is the datum for examining the gears involute measrrement instrument.To measue the involute prototype.We need more preeise method and device. This paper introduces the prineiples of testing involute prototype and the uneertainty of those instraments.emphasis on that developed at the Changchun Institute of Optics and Fine Mechanics.Results show that kind of instrument can be used for examining the first grade involute prototype of GB6467-86.