The three-axis turntable is the key equipment of the model coefficient calibration of the inertial measurement unit. Its integrated pointing error will affect the calibration test and reduce the application accuracy of the inertial measurement unit. For practical engineering application, based on the black box analysis method, the simulation analysis and data mining are carried out, and the rule of test error caused by the integrated pointing error is studied. According to this, the optimal discrete calibration method of inertial measurement unit based on the UOT three-axis turntable is arranged. Through tests on 24 positions and 6 rotations of 5 initial states, the calibration error is restrained to the greatest extent with the shortest calibration time, and the calibration accuracy is significantly higher than the traditional method, which has important engineering application value.