The Spherical Grating Monochromator(SGM)branch of Spectral Radiation Standard and Metrology(U27)beamline is specially built for measurement of the properties of optical elements and detectors.In order to accurately measure the performance of optical elements,higher-order harmonics must be suppressed efficiently.For the existing beamline where the design cannot readily be altered,the simplest method is to use transmission filters to suppress higher-order harmonics.With a 840 1/mm transmission grating used behind the exit of SGM in U27 beamline,the exit beam can be dispersed and the contributions of the different orders can be analyzed.Results of higher-order suppression by 200 nm,400 nm,600 nm thickness Al filters,100/50/200 nm,100/50/150/150/250 nm thickness Si3 N4/Mo/Si,Si3N4/Mo/Si/Mo/Si multilayers and Al/Mg/Al filter in the region of 13～43 nm show that when the thickness of Al filter is 400 nm,and the wavelength is between 17 nm and 33 nm,the contributions of higher orders to the detector signal intensity are less than 2% ,and the detector intensity is strong enough when the beam on.After being corrected by quantum efficiency of the detector,higher order contributions are less than 0.6%.Si3N4/Mo/Si/Mo/Si filter can be efficiently used to suppress higher-order harmonics in the region of 13～19 nm,and Al/Mg/Al filter can be used to suppress higher-order harmonics in the region of 30～43 nm efficiently.These are important for the accurate calibration of absolute reflectivities of multilayer and detector etc.