In order to decrease the corrosion rate of the pure magnesium and improve cell affinity of magnesium materials，polydopamine ( PDA) films and Mg ( OH) 2-PDA composite films are deposited on the pure magnesium surface． The optimum process of two kinds of films is investigated by the single factor experiment． The effects of DA mass concentration and film-forming time on film morphology and corrosion resistance are analyzed by field emission scanning electron microscope and dynamic potential polarization method． The chemical structure of the two films is studied by Fourier transform infrared spectroscopy． The results show that the optimum technological conditions for the preparation of PDA films is DA mass concentration of 1. 0 g /L，and the film-forming of 12 h; the optimum technological conditions for the preparation of Mg ( OH) 2-PDA composite films are the DA mass concentration of 1. 5 g /L and the film-forming time of 20 h． The corrosion resistance of the substrate is significantly improved under the optimum process parameters，and the corrosion resistance of Mg ( OH) 2-PDA composite films is the best． The obtained PDA films on pure magnesium have obvious crack defects． The microstructure of Mg ( OH) 2 films obtained by water heat treatment can provide a better site for the binding of polydopamines，which results in a more uniform polydopamine film．