Filter is widely applied in the motion controller field, for its main contribution to the improvement of motion controller in performance. In the first, different kinds of filters used in motion controller and their functions in the control loop were presented. Then the first-order low-pass filter and the second-order one were introduced in detail. The characteristics of each kind were analyzed, and the differences between them were pointed out. The notch filter was presented at length, and its model was obtained that was suitable for application in engineering, and an example was given. It concludes some important points when a filter is applied.