The new experimental measurement system is set up to measure light intensities scattered from the reflection-mode random surface. By using the technique of data average and overlay connection, the functions of scattered light intensity profiles are calculated at different incidence angles (45°～85°) on random surface. The results show that the full widths at half-maximum of intensity profiles are decreased gradually with increased of the incidence angles. While the incidence angle increases to a certain value, the light intensity scattered profile presents a central bright spot. Based on the symmetric decline function in mathematics, the relationship between the full width at half-maximum of intensity profile and the light wave vector is deduced, and the roughness exponent of self-affine fractal surface is extracted from angle-resolved scattered light intensity profiles. It is obvious that the obtained value of roughness exponent is in good agrement with that measured by atomic force microscop.