Abstract <p>Magnesium metallurgy is a potential technology for inclusions regulation. The physical parameters of inclusions are closely related to the quality of steel rails. With the help of Factsage thermodynamic software, the liquidus and solidus temperatures of steel and the generation temperature of typical inclusions are predicted, and the physical parameters of inclusions and deformations of horizontal and vertical treads of the head of industrial material U75V heavy rail steel were analyzed. The results show that an increase in magnesium content leads to an increase in the precipitation temperature of manganese sulfide, and incorporation of magnesium into Ca–Si–Al–O inclusions can lead to an increase in the inclusions generation temperature. The addition of magnesium to the steel not only optimized the physical parameters of inclusions, but also reduced the aspect ratio of inclusions by the value of ~4.84–5.83 before and after the magnesium treatment on the horizontal tread. Before and after magnesium treatment, the magnesium content of the vertical tread increased by 4.33–6.95, and the number of large-size Ca–Al–Si–Mg–O inclusions decreased before and after the magnesium treatment. In addition, the evolution mechanism of magnesium on inclusions deformation is described.</p>