The experimental setup for the measurement of aluminium diffuser′s bidirectional reflectance distribution function has been established by choosing a proper illuminating and viewing method. Characteristics of aluminium diffuser′s bidirectional reflectance distribution function under different situation are studied in experiment. The change trends of bidirectional reflectance distribution function with wavelength of different surfaces roughness of Al diffusers are different; after coated with Al+MgF2,the reflectance increase approximately from 1.5 to 3 times; from 200 to 280 nm, the relative bidirectional reflectance distribution function of Al diffuser does not change with wavelength, but it increases up to 13 percent while wavelength is longer than 280 nm. Contour plots resulting from experimental data show the change of aluminium diffuser′s bidirectional reflectance distribution function with different illuminating angles while viewing angles are fixed, a fitted empiristic formula in such case is given, its relative accuracy is 2.4 percent.