The primary purpose of this paper is to study the size effect of surface roughness and realize the quantitative description of the surface roughness in micro-forming process. This work is a continuation of the previous work by the authors. The effects of the initial surface roughness of the specimen, the grain size, and grain orientations on the surface roughness of micro-upsetting products were investigated. The ratio of the number of grains of the surface layer to the total number of grains was adopted to characterize the size effect. The variation of the size effect on the contact normal pressure during the compression process was also analyzed. And the quantitative description of the evolution law of surface roughness for micro-formed parts was realized. The corresponding micro compression experiment was done in order to testify the prediction model.