Cobalt sulfate and sodium borohydride were used to prepare the nano-Co-B alloy functional film by electroplating or electroless plating.The deposition rate by electroplating was faster than by electroless plating，with the influence of affecting factors the same for both electroplating and electroless plating.The higher the pH value and temperature，the faster the deposition rate，the higher the concentration of complexing agent，the slower the deposition rate.Also，deposition rate increased with increasing concentrations of cobalt sulfate and sodium borohydride，but decreased when the concentrations of cobalt sulfate and sodium borohydride exceeded a maximum value for electroless plating.XRD results showed that the nano-Co-B alloy functional film prepared was amorphous.The structure was not affected by the kind of plating method.SEM，STM and AFM showed that the amorphous film was formed by the secondary micrometres particles that were constituted by the initial nano particles.The particles were smaller by electroless plating.All particles for both methods were not larger than 3 μm.