Graft copolymer and method for preparing same

A method for preparing a graft copolymer pellet formed of a graft copolymer, the method comprising:

• (S1) polymerizing a conjugate diene-based polymer or an acrylate-based polymer with one or more among a vinylcyan-based monomer and an aromatic vinyl-based monomer to obtain a reaction product including a graft copolymer;
• and
• (S2) forming the reaction product in the form of a pellet through an extruder,
• wherein the reaction product comprises a dispersion medium including water, and
• wherein the extruder includes a barrel, a screw mounted inside the barrel, a ventilation part for discharging steam, and a heater part for heating the barrel,
• a hopper is coupled to one side of the barrel, and a discharge port for discharging the reaction product is on another side of the barrel,
• the screw has a plurality of forward zones alternating with a plurality of kneading zones, and
• the forward zones have forward direction threads, and the kneading zones have neutral-type threads or reverse direction threads.