Abstract: In order to increase the angular position measurement accuracy and improve structure design of a precise turntable, the angular position measurement precision of its azimuth shafting was detected. The error included axial error, encode error and other errors. Fourier harmonic analysis was adopted in data processing. Harmonic waves with different orders were used to fit the data, low order harmonic waves were removed, which could increase the position measure accuracy. Meanwhile, the error sources had been found. The error look up table could be used to correct the measure data afterward. As the result shows, the value of angular position measurement error after corrected is 1/4 of the value before corrected, the amplitude is about 0.8, the angular position measurement accuracy has been increased a lot. A look up table was built to correct post -measurement data; the error sources were found, which will help to improve the shafting structure.