Abstract: In order to measure optical components of large aperture in fine grinding process, the relationship of the contrast of interference fringes and the surface roughness was described by rigorous mathematical analysis based on the electromagnetic scattering theory. The mathematical derivation was verified with experimental data at different roughness. 280# rough sphere with aperture =1130mm, curvature radius R=3600mm, was measured by using the infrared interferometer. When a large aperture rough sphere was measured, the alignment method of infrared interferometer was introduced. The result shows that the rough sphere has obvious spherical aberration. The PV value of the rough sphere is 0.526 (=10.6m), and the RMS value is 0.117 (=10.6m).