The specialized flame-retardant masterbatch for extruded polystyrene board is produced by plasticizing and pelletizing methyl octabromide with polystyrene as the carrier, achieving a flame-retardant content of 55%. It combines the excellent flame-retardant properties of methyl octabromide powder with the advantages of good dispersibility, low additive requirement, easy foaming, easy extrusion, stable production, and environmental friendliness. Suitable for various extruded board production equipment, it features uniform pellet shape and size, is dust-free, and minimizes contamination to equipment and the environment.