S1, smelting high-manganese steel with scrap as a raw material by using an electric arc furnace, carrying out oxidative dephosphorization after the scrap is melted, removing oxidative dephosphorization slags after dephosphorization to obtain a molten steel I, crushing after cooling the oxidative dephosphorization slags obtained and putting into a slag ladle for later use, and transporting the molten steel I obtained via a ladle to an LF ladle refining furnace when a temperature is within a range of 1,460-1,580 degrees Celsius;

taking medium-carbon ferromanganese as a raw material, and taking 20% of a mass of scrap for electric arc furnace smelting of high manganese steel as an additive amount, heating up the medium-carbon ferromanganese to a molten state by using a mediate-frequency induction furnace, and holding the medium-carbon ferromanganese in the molten state at a temperature of 1,300° C.-1,400 degrees Celsius; wherein a C content in the medium-carbon ferromanganese is 1.0%-2.5% of a total mass of ferromanganese;

S2, adding a first slagging agent to the LF ladle refining furnace to prepare reducing slag after the molten steel I arrives at the LF ladle refining furnace, then adding a reducing agent into the LF ladle refining furnace for pre-deoxidation to obtain a molten steel II, wherein an amount of the first slagging agent is 1.5%-2.0% of a mass of the molten steel I, an amount of the reducing agent is 0.1%-0.2% of the mass of the molten steel I; the first slagging agent is a mixture of CaO, CaF₂, SiO₂, and Al₂O₃, and a mass ratio of each substance in the mixture is: CaO accounts for 55%-65%, CaF₂ accounts for 20%-30%, SiO₂ accounts for 5%-15% and Al₂O₃ accounts for 2%-10%;

adding a second slagging agent into the mediate-frequency induction furnace, wherein an amount of the second slagging agent is 1.5%-2.0% of a mass of the medium-carbon ferromanganese, the second slagging agent is a mixture of CaO, CaF₂, SiO₂ and CaC₂, and a mass ratio of each substance in the mixture is: CaO accounts for 60%-70%, CaF₂ accounts for 0%-15%, SiO₂ accounts for 10%-20%, and CaC₂ accounts for 5%-15%;

S3, adding a SiCa alloy into the mediate-frequency induction furnace after forming covering slags in the mediate-frequency induction furnace, with an amount of the SiCa alloy being 0.5%-1.0% of the mass of medium-carbon ferromanganese, reacting for 10-20 minutes for reductive dephosphorization;

S4, removing reductive dephosphorization slags in the mediate-frequency induction furnace to obtain a molten ferromanganese after a reaction of the reductive dephosphorization in the S3 is completed, holding the reductive dephosphorization slags at a temperature of 1,350-1,450 degree Celsius and pouring into the slag ladle of the S1 stored with the oxidative dephosphorization slags;

S5, adding the molten ferromanganese obtained in the S4 into the molten steel II obtained after S2 treatment, holding the molten steel at a temperature of 1,460-1,580 degree Celsius, and continuing a reduction refining in the LF ladle refining furnace for 10-15 minutes;

S6, determining currently a Mn element content in the molten steel, if the Mn element content is lower than the composition requirements of steel grades, adding medium-carbon ferromanganese into a current molten steel and smelting for 3-7 minutes until the Mn element content meets composition requirements of steel grades, then carrying out S7, wherein an addition amount of the medium-carbon ferromanganese is determined by a following formula:

if the Mn element content meets composition requirements of steel grades, then carrying out S7 directly,

the composition requirements of steel grades are: C accounts for 1.00%-1.20%, Si accounts for 0.40%-0.60%, Mn accounts for 10%-15%, P accounts for less than 0.030% and S accounts for less than 0.010%; and

S7, holding the molten steel at the temperature of 1,460° C.-1,580° C., adding the reducing agent described in the S2 for final deoxidation and tapping, with an amount of the reducing agent being 0.018%-0.022% of a mass of the molten steel.