For high-power laser facility, sub-beams caused by multiple defects of opitcal component surface with different distributions interfere with each other in the transmission process, bringing about complex changes in beam quality. So it is necessary to make a clear limitation on relative position of defects. On the basis of the diffraction transmission theory, when there are scratches with different spatial distributions on the optical element surfaces, the changes of beam modulation are studied. The influence of scratch depths on the distribution of near field beam modulation is also taken into account. Results show that when two parallel or vertical scratches are on the same or different surfaces of an element. Both of them produce more serious modulation than single scratch, and the maximum modulation degree can be increased to 1.5 times. Meanwhile more strict requirements for scratch depth are put forward. The results can provide reference for the revision of optical element standard and the determination of defects specifications for large- diameter elements in high-power laser systems.