The preparation process of thin silicon foil used to study the spatial nonuniformity in the laser driven intensity was introduced. Oxidation, diffusion, photoetching process and etching technology were adopted to achieve thin silicon foil with a thickness of 3 to 4 micrometers. The surface roughness was about tens nanometers and the grain size of silicon film was nanometer scale. The preparation parameters were studied to control the roughness of thin silicon foil.