Abstract: For most reflective images, scanning of the light field is carried out by a scanning mirror drum, so back scattering light from the reflective mirror, which is illuminated by a laser beam, brings inevitably about a Doppler frequency shift. In this paper, the dynamic echo characteristics of an IR thermal camera, which was illuminated by a laser beam, are analyzed. Selfmodulation of “cat eye effect” is also present. An experiment was designed to measure the Doppler frequency shift of the rotary mirror drum. The analytical results have been proved with a laser radar trace system.