The invention relates to a molten steel furnace external refining agent which belongs to molten steel furnace external treatment, in particular to an additive for desulfurizing, dephosphorizing, changing an inclusion state and improving the purity of steel in the molten steel furnace external refinement and a production method thereof. The refining agent comprises the following components in percentage by weight: 8-18 percent of CaO, 30-45 percent of Al2O3, 10-50 percent of SrO, 5-10 percent of CaF2, 1-4 percent of Mal, 0-2 percent of metal Mg, 2-6 percent of C, 2-7 percent of adhesive and the balance of impurities. The average desulfuration rate etaS is between 60 percent and 80 percent, and the average dephosphorization rate etaP is between 9 percent and 20 percent; the steel includes 90-120ppm of Al2O3 and 1.0-1.7ppm of CaO. The production method of the refining agent comprises the steps of selecting materials, grinding, mixing the materials, uniformly mixing, granulating, roasting, cooling, weighing and packaging to prepare a granular material ball. The invention has obvious desulfurizing and dephosphorizing effect by adding the SrO, can favorably remove inclusions in molten steel and strengthen the dynamic and thermodynamic performance of products by adding a small amount of metal Mg, MAl, C, and the like, has simple equipment and process and convenient production and can be produced at a large scale.