In order to explore the influence of the velocity measurement with encoder on the closedloop control system, it is better to use the encoder to improve the speed and control effect. In this paper, the principle of encoder speed is first described. Then, the influence of encoder resolution and sampling period on velocity estimation is analyzed. Then the closedloop control system is analyzed, the speed bandwidth under the change of encoder sampling frequency has no influence on the position of signal measurement; and to meet the system bandwidth conditions, the encoder sampling frequency is larger, the error caused by velocity measurement is finally verified by experiment, the sampling frequency of the encoder effect of the whole closedloop control system.