Abstract: The removal of inclusions in steel has always been a hot topic in the field of clean steel, and it is important for improving the quality of steel and guaranteeing product performance. Inclusions in steel are mainly removed by allowing them to float to the top slag and get absorbed in it. This removal process can be subdivided into three steps: growing up and floating in the molten steel, separation through the steel-slag interface, and dissolution in the liquid slag phase. Owing to the difference in physical properties of a steel-slag system and its interfacial characteristics, incompatible inclusions cannot be separated by crossing the interface, making this step a key factor for the inclusions’ removal. Moreover, this step occurs with the rapid physical transition of the steel and slag phases along with physical and chemical phenomena in parallel as well as the presence of high temperature, opaqueness, and other characteristics of the impact, making the study more challenging. In recent years, with the advancement of technologies such as numerical simulation and high-temperature equipment, the study of the behavior of inclusions crossing the interface has gradually increased. The classical force analysis model can predict the interfacial behavior of inclusions semiquantitatively and has a certain guidance role for slag system optimization. The computational fluid dynamics (CFD) model has advantages in the study of interfacial phenomena of inclusions, but it is still in the early stage of research. In the future, it is expected to expand to a larger scale, including more behavior scenarios and phase states. The combination of water and numerical models is an effective method to study interfacial behavior. The simulation results at a microscopic scale will be further extended with the advancement of experimental technology in the future. The high-temperature confocal in situ observation is the most direct research method, which is extremely helpful to understand and reveal the interfacial behavior of inclusions. Furthermore, it is expected to reveal the key mechanism of inclusions removal in a more complete and in-depth manner through equipment improvement in the future.