To evaluate the dynamic performance of the scanning mirror, a dynamic autocollimation method is presented. The scanning mirror under test and the rotating mirror for target simulation fixed on the dynamic target are skillfully incorporated into the collimated beam propagation path of a dynamic autocollimator, constituting a close loop of optical auto-collimation measurement. The measurement system of performance inspection for the scanning mirror based on dynamic autocollimation is designed, and the calibration method for the accuracy of the dynamic target based on autocollimation is introduced. Experimental results show that the dynamic accuracy of the autocollimation measurement system is ±15 μrad in the 360° rotation range, and the maximum velocity and acceleration available for test are 80°/s and 50°/s2, respectively. The test method and device are used to test the dynamic performances of each axis individually of the scanning mirror adopted in a space laser illumination imaging tracking system. Related test data including wobble of shaft, step response, and continuous tracking are acquired, which will provide reference and help for the performance improvement of the scanning mirror.