A wideband metasurface for RCS reduction is introduced in this paper. The surface is composed of similar type of metamaterial units with different geometric dimensions, leading to various reflection phases under the incidence of plane waves. By carefully choosing the phase distributions, diffusion will be produced for the reflected waves which may redistribute the scattering energy from the surface toward all the directions. Compared to the metal plate, the RCS can be reduced by 2-10dB in 9.5GHz to 13.5GHz.