The invention provides a method of reusing an inert gas in a polymer production plant by removing impurities such as a polymerization solvent and polymerization monomers from an inert gas discharged from a polymer production plant. The method of reusing an inert gas comprises a step of adsorbing and removing a polymerization solvent and polymerization monomers contained in an inert gas by passing, through an adsorbent layer, an inert gas discharged from a polymer production plant, wherein an inert gas reaching a predetermined purity by removing the polymerization solvent and polymerization monomers in the step of adsorption and removal is reused in the polymer production plant.