The invention relates to a method for preparing an Al-Ca alloy, which comprises the steps as follows: (1) in the charging step, quicklime containing CaO more than 85 percent or calcium carbide containing CaC2 more than 85 percent is added to a tubular furnace or an induction furnace in a graded manner, then metal Al is added according to a certain proportion for one time, argon gas is pumped into the furnace, a stirring device starts to stir when the temperature reaches above 1200 DEG C, and the flow rate of argon gas is 0.10 to 0.2L/min; (2) after the charging is completed, the temperature rise continuously until 1450 DEG C is reached, refining is carried out under the constant temperature, and the refining time is 20 to 30min; and (3) in the cooling-finishing step, power is cut off and cooling is performed after refining, finishing is carried out after complete cooling under argon protection, and adhered entrapped slag is removed by hand. The Al-Ca alloy can be not only used as deoxidation, desulphurization and occluded foreignsubstance denaturants, but also used as matrix alloy material for manufacturing cored-wires or complex alloys through further processing according to the steel variety requirements and process conditions.