Sampling period has important influence on the control performance of digital servo control system, and the sampling period is determined by a lot of factors including servo stability, hardware, interfering signal and so on. Shannon sampling theorem is only a guiding principle to choose sampling period. According to the sampling theorem, the higher the sampling frequency of digital control system, the closer of the control effect of the discrete control system to the continuous control system, but in practical applications, if the sampling frequency is too high and the sampling period is too short, it may not be able to perform complex control algorithm and complex rule of the motion control. It may lead to instability of the system because of the addition of zero order retainer during the process of discretization, and it cannot obtain the optimal effects of PID controller if the sampling period is too long or too short, and in order to restrain the interference signal effectively, it ask for different sampling period because of interference signal has different frequency size and it may be a narrowband or a broadband.