Abstract: Based on our achievements and that of peers of home and abroad, several aspects of nodular defect are summarized and reviewed. The size, shape and surface properties of nodule seed determinate the size, boundaries continuity and topography of nodule. The seed sources are mainly the residue during the processing and cleaning of substrate, contamination from the coating chamber and particulate from the evaporation source material. The corresponding methods to eliminate the seed source are given. The electronic field enhancement is another main reason for the damage susceptibility of nodule. Laser conditioning and mitigation method can improve the capacity of laser damage resistance.