The noise origin of attenuation system is explored by analyzing the wedged plate attenuator based on Fresnel transmission through two pairs of wedged plates. Multiple reflections between two surfaces of a pair of wedged plates introduce fluctuating error into the attenuation of the wedged plate attenuator and wavefront distortion of the exit laser beam. The attenuation and the radial light intensity distribution of the laser beam considering the effect of multiple reflections are calculated when the wedge space varies. And the calculation results show that wedge space between a pair of wedged plates has important influence on laser beam quality. The fluctuation of attenuation decreases but the distortion of wave-front becomes more complicated with the wedge space between the two parallel surfaces of wedged plate pairs increasing.