A phosphating agent, a metal component, and a surface phosphating treatment method therefor. The phosphating agent is used for the surface pretreatment of the metal component. Based on 1000 parts by weight, the phosphating agent comprises the following components in parts by weight: 5 to 30 parts of phosphoric acid, 3 to 10 parts of zinc oxide, 0.5 to 3 parts of molybdenum salt, 0.5 to 5 parts of magnesium oxide and the balance water. The film layer formed by the phosphating agent has a fine structure and strong adhesion, can produce a continuous, uniform and colored phosphating layer on the surface of the metal component, and is applied to phosphating treatment on the surface of a cold-rolled plate, a hot-rolled plate or a steel angle before spraying. The phosphating solution has a long service life and produces no waste water, and the phosphating can be carried out by means of by brushing, dipping, spraying or a combination thereof. The drying manner may be dying or a nature air-drying at a temperature ranging from 10ºC to 50ºC, and accordingly, energy consumption is reduced to a great extent, the phosphating time is short, extra surface conditioning is not needed before use, a promoter also does not need to be added, and the operations are simple and time-saving.