Gears are important basic parts and transmission components in machinery manufacture field, which are used in many aspects of modern industry. Improvement of gear manufacturing quality is based on many factors, and accuracy of instrument for measuring gear is one of important factors. In accuracy indexs of involute gears, tooth profile error is difficult to measure. The available methods for measuring involute tooth profile include specification curve mode, generation mode and coordinate mode, etc. The methods above can measure involute teeth profile of level 2 (GB/T10095.1-2001) gears at most, and cannot be used to measure level 1 gear.Measuring technology of level 1 involute is researched in this paper, and accuracy of the instrument for measuring reference level involute is highest in all instruments for measuring involute. This paper designed measuring support, and analyzed and verified the accuracy of minimal displacement transfer level. Manufacture compensation method was used to assembly base discs, gear and core shaft, and measuring error caused by component's eccentricity is reduced. By analyzing measurement error made by deviation of stylus, tooth profile angle comparison method and error compensation method are used to adjust situation of stylus, and adjustment accuracy are 10μm and 15μm, which accords with measuring specification of level 1 gear. Elastic creep between base discs and guide is analyzed, and creep rate is computed.All the measuring errors in the instrument are analyzed, and measurement uncertainty is evaluated by GUM. By comparing the instrument's measuring uncertainty and tolerance of level 1 involute, the instrument accords with measuring specification of level 1 gear. Because compensation relation of some measuring errors cannot be embodied when GUM evalutes measuring uncertainty of instrument, mont carlo method is used to evaluate the instrument's measuring uncertainty, which makes evalution result close to true value.In the paper, data acquisition and processing system is developed, and evalution interval of tooth profile, outlier's processing and acquisition interval are analyzed.By analyzing measuring error of the instrument, error compensation model is established, and diameter's error of base disc and eccentricity of components are compensated. Measuring accuracy of the instrument for measuring reference level involute is increased greatly after compensation. Finally, level 1 gear's tooth profile is measured, and measuring result is compared with gear measuring center's (Klingelnberg P65) measuring result in national metering institute. By comparing accuracies of instruments in national institutes, the instrument for measuring reference level involute is regard as the highest accuracy instrument.