This study focuses on the effects of plating additives and forced convection on microstructure and surface roughness of a copper foil at high current densities. A pilot Cu plating bath was designed according to the simulation of flow field using COMSOL Multiphysics. Accordingly, accurate fluid flow rates and the streamline patterns thereof were obtained in this work. The surface roughness of copper deposit depended on the limiting current density of cupric ions, the distribution of adsorbed chloride ions and the adsorbed organic additives at high current densities (10∼60 A·dm−2). Forced convection has strong influence on these factors as mentioned above. A copper foil with low surface roughness could be consequently obtained for the application of high frequency transmission in printed circuit board industry.