An experimental system for infrared spectral emissivity measurements is reported in this study, which enables the measurement of spectral emissivity of opaque solid materials in the temperature range between 473K and 1273K and spectral range from 0.8μm to 2.2μm. Emissivity characteristics are investigated for several Al6061 samples with different roughness and temperatures in atmosphere environment. By analyzing various uncertainty sources in this experiment, the combined uncertainty of the system is less than 3.9%. The influences of wavelength, temperature, surface roughness, heating time and oxidation on the spectral emissivity are discussed. The experimental results show that the spectral emissivity decreases slowly with the increasing of the wavelength, then the values at high temperatures are larger than that of low temperatures. The spectral emissivity increases with the increase of surface roughness. At a specified temperature, the influence of the heating time on the spectral emissivity is discussed. The spectral emissivity has a slight increase with the increasing of heating time due to oxidation, and the variation of the emissivity becomes negligible after 400 minutes of heating when the film thickness is stable.