Abstract: The working principle and main functions of the high-temperature confocal scanning laser microscope (HT-CSLM) are introduced. The detailed summary of the recent research progress in the aggregation of inclusions using the HT-CSLM is provided. This includes in-situ observations of collisions, aggregation and growth of inclusions on the surface of molten steel, slag and at the steel-slag interface, as well as dynamic studies and model derivations. 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. Ideas are also provided for the future research direction of high-temperature confocal microscopy in the field of inclusion collision.