Splitting angle is one of the significant performance parameters of diffractive laser beam splitter. Current study of wide-angle diffractive beam splitter mainly focuses on Dammann grating. Dammann grating relies on its periodic transition points to modulate the incident optical wave, however the inhomogeneity of outgoing beams is extremely sensitive to the precision of transition points, and the existing processing technology cannot meet the requirement of design accuracy. So, using a sub-wavelength multi-level structure to achieve wide-angle beam splitting is put forward and an actual design example of sub-wavelength 16 levels grating is given, whose incident wavelength is 1.55 μm, beam splitting number is 16 and diffraction angle is 29°. Getting an initial structure by scalar diffraction theory and then applying rigorous coupled- wave analysis and genetic algorithm to do a vector optimization, finally the diffraction efficiency rises to 89%, inhomogeneity drops to 4.53%. The results indicates that sub-wavelength multi-level structure can achieve wide-angle beam splitting with high diffraction efficiency and homogeneity.