A metal surface treatment agent is characterized in that the metal surface treatment agent comprises the following components of, by weight, 0.5-8.0% of a corrosion inhibitor, 2.0-9.0% of a surface active agent, 2.0-8.5% of chitosan, 0.1-1.0% of an antioxidant, 1.5-9.0% of titanium dioxide, 1.5-9.0% of silicon dioxide and the balance water. A preparation method of the metal surface treatment agentcomprises the steps that the 0.5-8.0% of the corrosion inhibitor is stirred with the 2.0-9.0% of the surface active agent; after 20% of the water is added to be sufficiently mixed, heating is conducted till the temperature reaches 50-60 DEG C; sufficient stirring is conducted, and then 2.0-8.5% of the chitosan is added; and stirring dispersion is conducted to obtain a stable solution, then 0.1-1.0% of the antioxidant, 1.5-9.0% of the titanium dioxide, 1.5-9.0% of the silicon dioxide and the balance water are added, sufficient stirring is conducted, and the metal surface treatment agent is obtained. According to the metal surface treatment agent, the metal surface can be effectively cleaned, and a protective film is formed on the metal surface to protect glossiness of the metal surface.