The As2Se3 specimens with different thicknesses, roughnesses and surface smoothnesses are prepared by use of homemade As2Se3 glass rods. The refractive indices are measured by the infrared spectroscopic ellipsometer, and an optical model is built to obtain the refractive indices by fitting. The influences of thickness, roughness and surface smoothness on the refractive indices of specimens are comparatively analyzed. The results show that all factors have obvious influences on the measurement accuracy of the ellipsometer and the surface smoothness is of most importance. If the specimen thickness is controlled to be 1-3 mm, and simultaneously the back side roughness and surface smoothness of specimens are increased, the measurement accuracy of the ellipsometer can be obviously enhanced.