Like other beam lines of synchrotron radiation light sources, the Spectral Radiation Standard and Metrology beam line (U27) of Hefei synchrotron radiation light source has the difficulty of higher order of hamonics (HOHs). Though the HOHs in the region of 10-45 nm have been suppressed effectively using transmission filters, such as Zr (with the thickness of 200nm), Si3N4 (100nm), Al (200nm) and Mg (250nm), the HOHs in the region between 45-105nm are existing. Enables the suppression of the HOHs For the configuration of the existing beam line cannot be readily altered, At present, the lamellar grating with Au films is illuminated in the incidence configuration. The characterization of the suppressing the HOHs can be improved by optimizing the grating coating or substrate material and the profile parameters, which is the focus of our research. Moreover, the combination of the grating design with the film filters will We in order to realize the function of suppressing the HOHs. The following show the simulation of the diffraction efficiencies of a SiC grating with a 200lines/mm as a function of the profile parameters.