To correct and improve calibration and measurement precision of optical element performance at 5—140 nm waveband covered by metrology beamline, a scheme for higher-order harmonic suppression was designed based on spectral radiation standard of State Synchrotron Radiation Laboratory and distribution of higher-order harmonic of the metrology beamline. The distribution of the higher-order harmonic of metrology beamline at 5—140 waveband was studied by use of 3 500, 840 1/mm gold-film self-support transmission gratings and a photodiode detector. Thus a method to suppress higher-order harmonics at different wavebands with Si, Al, Al/Mg/Al filter and LiF window and MgF2 window was put forward. Experimental result shows that the content of higher harmonic without filter is extremely low in 5—15 nm waveband, the proportion of higher-order harmonic with quantum efficiency corrected by detector can be suppressed below 1.8% in 5—40 nm waveband when proper filter is added at the corresponding waveband; LiF window and MgF2 window can basically make higher-order harmonic proportion zero in 105—140 nm and 115—140 nm wavebands. The scheme for suppression of harmonic waves with filters at whole waveband is effective.