Aiming at the problem of mechanical resonance in the mirror for 1/2 mechanical transmission process, put forward the mechanical resonant reduced or eliminated mechanical resonant method. Through the analysis of the reflector stable system control structure model, and deduced the transfer function and dynamic equation, combining the actual structure the reflector, analyzes mechanical resonant emergence mechanism, discussion on the resonance frequency and mechanical structure mirror stable servo system in a relationship, and taking certain type tank length mirror as example progress validate analysis. The results show that the system doesn’t appear instability of the structure design of the phenomenon, should take reasonable design and the beginning of more advanced simulation, to suppress or eliminate mechanical resonant.