The invention provides a preparing method of low-silicon pre-melted slag for electroslag remelting. The preparing method comprises the first step of even slag charge mixing, the second step of slag smelting and the third step of aluminum iron alloy adding and smelting. According to the preparing method of low-silicon pre-melted slag for electroslag remelting, the requirement for equipment is low, operation is easy, control is convenient, and cost is low. The problem that Al, Ti and elements prone to oxidation are burned down in the electroslag remelting process can be effectively solved.