International standard ISO 10110-7 sets a strict limit on the size and quantity for surface defects of an optical element. For high-power laser, sub-beams caused by defects with different distributions interfere with each other in the transmission process, causing beam quality complex changes. So it is necessary to make a clear limitation on relative position of defects, thereby giving the standard a more comprehensive supplement. Based on the diffraction theory, the changes of beam modulation are studied. The influence of scratch depth on the distribution of near field beam modulation is also taken into account. Results demonstrate that when two parallel scratches are on the same or different surfaces of an element, they produce more severe modulation than single scratch, and the maximum modulation can be increased to 1.5 times. Meanwhile more strict requirements for scratch depth are put forward. The results could provide reference for the determination of defects specifications for large-diameter optical elements in high-power laser systems.