Aiming at the problem that the smooth metal furnace edge of the test sample support platform has extremely strong scattering during the reflectance test of high-temperature materials, resulting in a greatly reduced reflectivity test accuracy, a method of structural transformation of the heating furnace edge is proposed, and different depths and widths are designed. RCS simulation of the scaled model of the designed structure is carried out through the FEKO software on the V-shaped and U-shaped furnace edges of the furnace. The simulation results of three incident angles show that the V-shaped and U-shaped groove edges of depth 2 have obvious RCS reduction effects at the frequency points in the frequency band around 24-40 GHz. Compared with the flat furnace edges, the V-shaped and U-shaped groove edges have a significant RCS reduction effect. The furnace edge has been reduced by about 8.6dB and 9.8dB respectively, which indicates that the reflectance test of the material after the structure optimization can improve the test accuracy.