On the basis of presenting structure, control principle and control algorithm of acquisition, tracking and pointing (ATP) fine tracking subsystem, the semi physical model is built to analyze the tracking performance of digital to analog converters with different resolution, and the tracking contrast experiments are carried out on the same beam position and the beam after disturbance. Combined with the signal transmission of fine tracking control system, the effects of digital to analog converters with different resolution on the tracking accuracy of ATP system are analyzed. The experimental results show that the higher the resolution of digital to analog converter is, the better the tracking performance of the ATP system is. However, when a 14 bit digital to analog converter is used, there is little contribution to improve tracking accuracy even continue to increase the resolution. By analyzing the spectral component of spot centroid signal after tracking, we find that the resolution of digital to analog converter within frequency band and outside the disturbance suppression bandwidth is proportional to the corresponding spectral component, so it is necessary to improve the disturbance suppression bandwidth of fine tracking system to achieve high accuracy tracking.