HEMG (High-Efficiency Multi-beam Gratings) are widely used in optical systems as splitters. HEMG should have (1) high diffraction efficiency and (2) uniform intensities at each diffraction order. High efficiency is realized by making the phase grating. Uniform intensities may be attained by either W. H. Lee s PPM Pulse Position Modulation) or PWM (Pulse Width Modulation). However, when the number of the required uniform beams increases, or when we deal with certain kinds of 2-D HEMG, these two modulation methods will lose their effectiveness, and become either ???perfect or too complicated to be practical. In this paper, we introduce the iterative method to design HEMG. Some practical results are shown.