To explore the effect of different Mg contents on the morphology, composition, distribution, and deformation of sulfides in 49MnVS3 non-quenched and tem-pered steel, the inclusions were observed and counted by Zeiss metallographic microscope and scanning electron microscope, and the inclusions in the com-pressed samples were compared by Gleeble-3500 thermal simulation test ma-chine. Results showed that the size of sulfide in steel decreases and the distri-bution uniformity of sulfide are significantly improved with the increase of Mg content. The proportion of composite inclusions in steel increases obviously, and the proportion of individual MnS decreases. The composition of the included core is in accordance with the principle of Al₂O₃ → Al₂O₃ + MgO·Al₂O₃ → MgO·Al₂O₃ + MgO → MgO → MgO + MgS. After Gleeble compression, the aspect ratio of sulfide inclusions decreases, and the spindle ratio h increases significantly.