The fabrication of harmonic beam splitter for 532nm wavelength green light laser with dual ion beam sputtering(DIBS) technology was studied. The layers′ thickness was monitored by time. Against the half wave hole phenomenon, based on analyzing it′s forming mechanism, the group optimizing method was adopted to modify lays′ thickness. Then, the high quality harmonic beam splitter without half wave hole was obtained. It also presented a feasible method to modify layers′ thickness of irregular coating system monitored by time.