Disclosed is a combined treatment method for improving corrosion resistance of metal component in chlorine-containing solution. First, the metal component is placed in the chlorine-containing solution. Large-area overlapping laser shock peening without an absorbing layer is used, when laser pulses are irradiated on the target metal component, the metal matrix surface absorbs the laser energy, vaporizes and expands to form a high-temperature and high-pressure plasma, a chlorine-containing passivation film is formed, to improve the surface corrosion resistance of the metal component. After that, the surface layer of the metal component is subjected to surface polishing, followed by large-area overlapping laser shock peening with an absorbing layer at room temperature, to further improve the corrosion resistance of the metal component. The combined treatment method of the present invention can be applied to improve the corrosion resistance of metal components in highly corrosive chlorine-containing environments of seawater and the like.