Slag former for smelting polycrystalline silicon medium and use method of slag former

The invention discloses a slag former for smelting a polycrystalline silicon medium and a use method of the slag former. The slag former is formed by mixing the following raw materials by weight: 30%-60% of Na2SiO3, 20%-50% of SiO2, 1%-15% of TiO2 and 1%-5% of Al2O3. The slag former is added in a process of smelting and purifying the polycrystalline silicon medium, so that the partition coefficient LB value of boron in the slag former and a silicon solution is effectively increased by 1-2 from 2-4, the boron removal effect is improved, and the boron content of a silicon material is reduced to be less than 0.20 ppmw.