Abstract: In order to explore the microstructure change rule of low carbon sulfur free-cutting steel 1215MS in the process of hot delivery and hot charging at different temperature ranges, the thermal simulation test machine was used to carry out relevant research. The results show that the casting slab of low-carbon sulfur free-cutting steel 1215MS entered the steady-state cooling stage after solidification for 1 500 s, and the cooling rate during hot delivery was 0.15—0.25 ℃/s. Affected by the temperature difference between the core and the surface of the slab, when the hot charging temperature was between 652 ℃ and 888 ℃, the γ+α two-phase region would be formed inside the slab, and the hot charging in this temperature range would easily lead to the uneven structure of the slab. Although the dynamic recrystallization method of high temperature rolling could be used to eliminate the microstructure inhomogeneity caused by hot delivery and hot charging in the two-phase region to a certain extent, the overall effect was still not as good as that of cold charging billet.Finally, it was suggested that the hot charging temperature of low carbon sulfur free-cutting steel 1215MS should be controlled below 652 ℃, and the industrial production should be carried out under this condition. The microstructure and properties of the steel could be the same as those of the cold charging billet.