The invention discloses a slag-erosion-resisting fireproof material. A method for forming a slag-erosion-resisting coating on a surface of the material in situ comprises the following steps: taking aluminum oxide, silicon dioxide, calcium carbonate, magnesium oxide and calcium fluoride as raw materials, and preparing molten slag powder with the alkalinity of 0.9 to 4.0; heating the mixed powder to1550 to 1650 DEG C and melting down; taking a fireproof material as a negative electrode and graphite as a positive electrode, and immersing the negative electrode and the positive electrode respectively into the molten slag for 5mm; connecting the graphite and the fireproof material with a positive electrode and a negative electrode of a direct-current power supply through taking molybdenum barsas lead wires, so as to form an electrochemical circuit. Voltage is adjusted to 6 to 12V; after the fireproof material is electrified for a certain period (15 to 30 minutes), a slag-erosion-resistingcoating can be formed on the surface of the fireproof material in situ, and further erosion of the molten slag can be resisted. By synthesizing the slag-erosion-resisting coating in situ, the servicelife of magnesia carbon bricks is greatly prolonged, and the operation is simple; the production practical value is relatively high.