In order to improve the light energy utilization of equipment for measuring high-temperature optical parameters of materials and obtain better irradiance on the surface of the sample to be tested, a semi-ellipsoidal reflector is applied to the equipment. First, the equipment for measuring high-temperature optical parameters of materials and the role of the semi-ellipsoidal mirror in the equipment are introduced. Then, the optical characteristics and surface shape changes of semi-ellipsoidal mirrors are analyzed by using ray tracing and finite element analysis methods, and the influence of surface shape change of the semi-ellipsoidal mirror at 30 ℃ on optical characteristics is analyzed. Finally, the shape of the inner surface of the semi-ellipsoid mirror is measured by the three-coordinate measurement instrument, and the simulation results are verified. Experimental results show that: at 30 ℃, the root mean square (RMS) of the deformation of the semi-ellipsoidal mirror after removing ellipsoid deformation is 2.15 μm, the irradiation uniformity obtained by using a Φ15 mm blackbody radiation source is 61%, the energy utilization is 7.6%, and the RMS is 5.75 μm measured by the three-coordinate measuring instrument. This study provides a new way to measure high-temperature optical parameters of materials.