The Intensity—attenuator and imaging system with high attenuation used for measuring the far-field spatial intensity distribution of “Xiang Guang Ⅱ” laser system is introduced. Intensity—attenuator is an important part of the far-field real time detecting system for high power laser. The attenuation call vary from 10-2 to 10-12 and the induced wave aberration of attenuator and imaging system is controlled within the 2× diffraction limit. namely 2λ/3 wave aberration under given experimenta1 conditions.