Abstract: The working principle and the main functions of the high-temperature confocal scanning laser microscope (HT-CSLM) are presented. In situ observation of the evolution of high-temperature microstructure of materials can be performed using the HT-CSLM. This is important for studying in detail the processes of material melting, solidification, high-temperature stretching, martensitic transformation, etc. It can also be used in the metallurgical field to study the dissolution, collision, agglomeration, and growth behavior of inclusions. The recent advancements in the aggregation of inclusions using the HT-CSLM are summarized. In-situ observations of collisions, aggregation, and growth of inclusions on the surface of molten steel, slag, and at the steel–slag interface, along with the dynamic studies and model derivations, are included. The collision behavior of non-metallic inclusions at the steel/Ar interface has been analyzed using high-temperature confocal microscopy. This is an important parameter for understanding the collision, agglomeration, and growth behavior of non-metallic inclusions in steel and for exploring the methods to improve steel cleanliness. According to the law of agglomeration of inclusions at the steel/Ar interface, inclusions with similar phases exhibit attraction: the attraction between the solid phases is the strongest, followed by that of the semisolid–semisolid pairs and the liquid–liquid pairs. For inclusions with different states, both attractive and repulsive forces exist simultaneously. The difference between the forces depends on their physical properties, in particular, the contact angle between inclusions and molten steel. Research on the parameters of the capillary force model shows that the effect of the density, size, and contact angle of inclusions is significant on capillary suction, while that of the steel surface tension is relatively weaker. Previous studies have included Al₂O₃, Al₂O₃–SiO₂, Al₂O₃–CaO, MgO, Al₂O₃–MgO, Al₂O₃–Ce₂O_3, and Ca–, Si–, and Al-type inclusions in carbon steel. However, there has been limited research on other types of composite inclusions, such as Ti-type oxides and titanium aluminum spinel. The influence of different gradients of the same element on the collision between inclusions should also be taken into consideration. The current model for calculating the attractive force between inclusions is explored, and the impact of factors such as density, size, and distance on the trend of inclusion aggregation and collision in steel is analyzed. The scope for further research on the use of high-temperature confocal microscopy in the field of inclusion collision is also included. The K–P model for calculating the capillary force between inclusions at the steel/Ar interface still has many limitations: a large amount of physical property data, such as the contact angles between various inclusions and the molten steel, is required. This in turn makes the calculation of the magnitude of capillary forces between all inclusions on the surface of the molten steel difficult. Therefore, correcting the K–P model or establishing a new collision model for inclusions on the surface of molten steel is crucial in the study of the collision trend of inclusions on the surface of molten steel.