The invention discloses a device and a method for nondestructive testing of sulfide inclusions in steel. The device comprises an electrolytic cell, a low-temperature thermostatic control bath, a direct-current potentiostat, an argon bottle, a flowmeter, a pH meter, a computer and a plurality of cellulose acetate plastic bags 8. The method includes 1), making preparations for samples and preparing electrolyte by even mixing of anhydrous lithium chloride, gamma-butyrolactone, glycerol and absolute ethyl alcohol; 2), completing electrolysis preparations; 3), starting electrolysis, namely controlling a pH value of the electrolyte to be 7-9 by a citric acid solution, and electrolyzing for 12-36 hours; 4), washing the steel samples and the cellulose acetate plastic bags with the absolute ethyl alcohol, weighing the washed steel samples and subjecting washing liquid to magnetic separation; 5), conducting classified filtration under vacuum and separating out the sulfide inclusions. The device and the method have the advantages that Fe<2+> oxidization during filtration is avoided, filtering and collecting efficiency is improved, loss of the inclusions during filtration is reduced, and nondestructive extraction of tiny inclusions in the steel is achieved.