The invention provides a flux suitable for hot-dip galvanizing aluminium magnesium alloy. The flux suitable for the hot-dip galvanizing aluminium magnesium alloy comprises the following components: 2-14 g/L of potassium fluoroaluminate, 250-500 g/L of zinc chloride, 0-20 g/L of aluminum fluoride, 30-70 g/L of cerium chloride, 20-55 mL/L of ethanol, 5-20 g/L of citric acid and the balance of water;and pH of the flux is 4-5.5. The flux is heated to the temperature of 70-85 DEG C, and a treated matrix is soaked in the heated flux for 30-60 s, and then is taken out and dried; and the matrix is subjected to dip plating in zinc-aluminum-magnesium alloy liquid to obtain a surface galvanized aluminum magnesium alloy material. The flux does not contain ammonium chloride, and thus, ammonia gas andsmoke are not generated in a plating assisting manner; a plating layer is compact in bonding, excellent in shape and appearance and high in bonding strength, and surface skip plating can be preventedeffectively; the corrosion resistance of the plating layer can be ensured while the thickness is reduced; and the flux does not contain a surfactant, can be stored for a long time, is low in cost, andcan be reused.