Abstract: Surface roughness of silicon-on-insulator(SOI) nano-optical waveguide can significantly increase scattering loss. It is one of the problems to be solved urgently in different application fields. Firstly, the concept of surface roughness and the progress of theoretical research of surface scattering loss were introduced. Secondly, various advanced measurement methods of surface roughness of SOI nano-optical waveguide, including the problems existing in the characterization of surface topography, were reviewed. Thirdly, several kinds of surface smoothing processes were also introduced. Finally, some conclusions were presented combined with our study.