The illumination computational formula recommended by the International Commission on Illumination (CIE) does not adapt to the modern construction materials with mixed reflection characters. In order to find a new luminance computational method adapting to the modern construction materials and to save building energy and control urban nightscape luminance, 30 frequently-used construction materials with respect to various directions in photometric laboratory were measured. Then the luminance modified coefficient K(i,β) was figured out, and analysed the connection of reflection luminance and atmospheric attenuation in the process of divergence of light. The K(i,β) and viewing distance, light kinds, luminaire use, material cleanliness, maintenance condition of lighting system as modified coefficient was adopted to amend the computational formula of CIE, and then a new calculation model is derived. Through calculating and comparing, the luminance value of the new calculation model is one-third as much as that of the traditional one.