Servo system is widely used in NC machine tools and robots because of its high performance, high precision and other advantages. Due to the limited stiffness of the drive devices such as ball screw in machine tool, the flexible connection of the feed servo system is prone to cause vibration, which affects its stability and accuracy. Based on second-order state observer, a mid-frequency vibration suppression method with observational compensation for velocity disturbance was presented for the rotating feed servo system. The velocity observed by the speed observer was subtracted with the actual speed feedback, and the vibration signal was extracted by band-pass filter as compensation to the speed feedback, by which the system vibration was canceled, so the system bandwidth was improved and stability and accuracy were maintained. Finally, the validity of the proposed method is verified by simulation and experiment under different speed ring gains.