Spectral beam combining (SBC) laser systems are rapidly advancing the output power scaling for high-average-power beam-combined fiber lasers with near-perfect beam quality. Grating as the dispersive element requires high diffraction efficiency (DE) and broad bandwidth (BW) for improving the combined output power scaling. A broad BW high DE polarization-independent reflective multilayer dielectric (MLD) grating is designed. The -1st order DE of the designed grating exceeds 99.84% at 1053nm central wavelength. The BW of the grating with the -1st order DE higher than 99% is up to 99 nm for non-polarized incident light. This MLD grating can be used as a reliable combiner in the SBC system.