The invention provides a deoxidizing alloying agent capable of purifying molten steel and a preparation method thereof. The components of the deoxidizing alloying agent include, by weight percentage,30-50% of aluminum, 2-6% of silicon carbide, 2-6% of calcium aluminate, and 5-45% of one or more of niobium, vanadium, titanium, manganese, nickel, chromium, copper, molybdenum and silicon; and particle sizes are 5-50 mm. During preparation, metal aluminum and industrial pure iron can be melted in an induction furnace crucible according to the finished product content; the metal niobium, vanadium,titanium, manganese, nickel, chromium, copper, molybdenum and silicon can be added; spiral electromagnetic stirring can be simultaneously applied, the current of the spiral electromagnetic stirring is 150-250 A, and the frequency is 2.5-4 Hz; the silicon carbide and calcium aluminate fine powder can be added after the added metal is completely melted; the power supply of the induction furnace canbe stopped after 5-10 min of stirring; the spiral electromagnetic stirring can be continued until alloy is solidified; and a crusher can be utilized to crush alloy ingots into small pieces with a particle size of 5-50 mm, and packaging can be performed for later use. The full uniformization of the alloy and the silicon carbide and calcium aluminate fine powder can be guaranteed by adopting a spiral electromagnetic stirring technology; the full purifying molten steel of the calcium aluminate can be guaranteed; and deoxidizing alloying time can be saved.