In high power laser beam parameters measurement, attenuation scheme with high rate is key to far-field measurement. The far-field optical measurement system was analyzed and diameter of 95% encircled energy was used as important evaluation criterion of far-field measurement system. Measurement error of far-field optical measurement system and effect of attenuation with high rate on far-field measurement results were analyzed. Principle of attenuation scheme with high rate was established. By changing parameters of high attenuation rate in condition of single parallel plate, a pair of parallel plates and a pair of wedge flaps by Virtual Lab, influence of attenuation on the far-field measurement system was simulated and analyzed deeply. According to measurement system for f=3 000 mm and F=10, best attenuation scheme with high rate is designed. Diameter of 95% encircled energy of far-field image is 45.5 ?滋m, or 3.54 times of diffraction limitation.