The invention relates to the technical field of mineral wool production and discloses a steel hot molten slag mineral cotton and its making method. The raw materials of the steel hot molten slag mineral cotton comprise 70-90% by mass of molten blast furnace slag and 10-30% by mass of a tempering material. The making method mainly comprises the following steps: directly introducing the hot molten slag to the initial melting zone of a slag melting furnace through a slag tank, and allowing the tempering material and the hot molten blast furnace slag to enter the initial melting zone of the slag melting furnace together; and maintaining the temperature of a melt in the initial melting zone in a range of 1400-1500DEG C for 4-6h, then allowing the melt to enter a primary melting zone, maintaining the temperature of the melt in the primary melting zone in a range of 1420-1450DEG C for 6-9h, then allowing the melt to enter a material discharge zone, and allowing the melt to flow to the roller of a centrifuge to form raw cotton. The preparation method has the advantages of energy saving, consumption reduction and simple process flow, and the prepared mineral cotton has the characteristics of good vitreous state, high fiber formation rate, wide adjustment range of the acidity coefficient and the like, and can satisfy the diversification demands of the market.