Experimental investigation and kinetics model ware carried out to study the effect of the atmosphere on the desulfurization of low-sulfur plastic die steel during the electroslag remelting process. 55Cr17Mo1VN plastic die steel was applied as the electrode and remelted with two different kinds of atmospheres using a laboratory-scale ESR furnace. It was found that the sulfur content of 50 ppm in the electrode decreased to 8–12 ppm in the air atmosphere, while reduced to 9–14 ppm in a protective atmosphere. The desulfurization rates were 82% and 78%, respectively. Correspondingly, the sulfur content of 0.12% in initial slag increased to 0.125% and 0.15%.