Terbium metal was melted by DC arc plasma using pure Ar and Ar + H-2 mixture, respectively. The temperature distribution and the fluid flow during the melting process were simulated. Oxygen and nitrogen concentrations were examined by the inert gas fusion method. Experimental results show that the gaseous concentrations can be reduced more efficiently by hydrogen plasma arc melting (HPAM). Activated hydrogen atoms dissociated in high temperature plasma-arc probably take part in the refining reactions. The detailed behaviors of oxygen, nitrogen and hydrogen atoms are discussed systematically in this study. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.