The present invention relates to a method for producing a diene-based graft copolymer resin, and a diene-based graft copolymer resin produced therefrom, the method including: mixing an aromatic vinyl-based monomer, a diene-based rubber polymer, and a polymerization initiator to prepare a first reactant; mixing a vinyl cyan-based monomer and an antioxidant to prepare a second reactant; adding and polymerizing the first reactant and the second reactant into a polymerization reactor to prepare a polymer; and removing unreacted monomers in a devolatilization tank.