The near-field diffraction characteristics when a high-power laser beam traverses contaminant particles are studied by using the designing software of high-power laser drivers-Laser designer. The modulations generated by contaminant particles are sorted. Then the influence of contaminant particles with amplitude or phase modulation on the near-field intensity distribution in vacuum or in fused silica is analyzed in great detail. The results show that in both vacuum and fused silica, the phase modulated contaminant particles have a greater influence on the near-field properties of high-power laser. Moreover, it is found that in fused silica, the small-scale self-focusing hot-image modulation of high-power laser induced by phase modulated hard-edge contaminant particles is momentous. But the lateral shift of high-power laser beam caused by contaminant particles maybe inhibits the small-scale self-focusing effect to some extent, thereby reducing the laser injury risk of optical component.