This investigation concerns the effect of the process parameters on surface roughening during plastic deformation. The modeling is based on the assumption that surface roughness is proportional to the maximum shear stress on the surface layer. Therefore, an equation is developed in order to describe the relationship between the surface roughness and such process parameters as the initial roughness, grain size, effective strain, and maximum shear strain ratio on the surface layer. In a tensile test, the surface roughness increases nonlinearly with a normal anisotropic value and linearly with the effective strain or grain size. The surface roughness also increases nonlinearly with the effective stress and the strain hardening exponent under some fixed conditions. The normal anisotropic value must be considered in order to evaluate surface roughening during deformation. The experimental results support the proposed model. The proposed model improves our understanding of the mechanism of surface roughening in sheet metal forming.