In order to solve the problem the velocity oscillation of oscillating mirror,permanent magnet synchronous motor(PMSM) was used as a drive motor.System transfer function was established.Taking into account that the scan movement is periodical,a modified repetitive contorller was proposed to control the angular velocity of scan motor.This controller used two amplifiers to adjust the system gain.As a result,the tracking accuracy was improved.Experiments show that the controll system can efficiently improve the velocity stability of oscillating mirror,and damp the osccillation of scan motor when the scan direction is changed.