In order to solve the difficult problem of detection of pitch deviations of high-precision master gears, a new measuring instrument is developed. Detail description about measuring apparatus of pitch deviations developed for master gears was presented in the paper. Computer aided technology was used to deal with data collected by computer, and error analysis about the measuring apparatus was introduced, which affected measurement accuracy. The results confirm that the measuring apparatus is able to meet measurement requirement and improve efficiency through the measuring experiments on master gears of precision grade 2 and 1 with modulus 2 mm and 2.5 mm, respectively. And the uncertainties of single pitch deviation and total cumulative pitch deviation are 0.07and 0.26, respectively.