Scattering from 1 dimensional random rough surfaces with varying roughness was investigated by numerical integration based on Kirchhoff approximation.With the increase of roughness,scattering peak was shown to shift continuously from specular to backscattering direction,while its amplitude decreased and width broadened.The surface exhibited a nearly cosine scattering distribution within a narrow range of roughness and could be treated as a Lambertian body.Scattering peaks will remain at backscattering direction when the roughness is very large.