Polishing alloy aluminum sample′s specular reflection spectrum in waveband 0.5~1.5 μm is measured by spectrophotometer, then it can be extrapolated to the all band by using constant and power function extrapolation. According to Kramers-Kronig(K-K) method, complex refractive index and dielectric constant of this sample in waveband 0.5~2.5 μm are deduced, this result well coincides with ellipsometer′s data in waveband 0.5~1.5 μm. The rough alloy aluminum sample′s scattering bidirectional reflectance distribution function(BRDF) at 1.06 μm is calculated using Kirchhoff method and deduced dielectric constant, which well coincides with BRDF measurer′s data. Roughness parameters and dielectric constants extrapolated in waveband 1.5~2.5 μm is used to calculate scattering BRDF of the rough alloy aluminum sample in this waveband.