Abstract: The EO tracker servo system design focuses on the frequency-domain characteristic parameters of the video processing system.We analyzed the theoretical model of the video processing system in the frequency domain, and designed a novel testing method. By using the velocity loop of the optical tracker servo system，through the frequency sweep in frequency domain and the contrast of the signal phases as well as the amplitudes，we indirectly measured the time lag and bandwidth of the video processing system. Taking a 50 Hz video processing system for instance,the tested bandwidth is 19.452 Hz, the time lag is 40.57 ms.