Abstract: In order to research the influence of scratch defects on the quality of beam field in the high power laser system, the non-linear paraxial wave equation is calculated with the split-step-Fourier-transform method. With different parameters of scratch defects, the intensity distribution of the beam field is obtained by using numerical simulation. The simulation results show that the maximum and the contrast of the beam field intensity inside or behind optics increase with the increase of the length, width or depth of the scratch defect. The contrast of the intensity distribution of beam near-field also increases. For the intensity distribution of beam far-field, the spectrum energy corresponding to the width direction of the scratch is enhanced. The study can provide some quantitative analysis bases for the setting of the scratch detection criterion.