Statistics on reflective light intensity of rough surfaces is not only based on simple theory, but also able to give the most important features of rough surface scattering. The theoretic analysis and deduction of reflective light field of rough surface is performed, and the results suggest that the key features of reflective light field of rough surface is determined by the Fourier transform of rough surface highness distribution and the incident light field. In case of Gauss surface illuminated by uniform parallel light, the reflective intensity is a Gauss function of the effective roughness, and its distribution on the focal plane is a sinc square function.