Developments in the contents of different typical inclusions in 3104 alloy melt were described during heating and holding processing. The settling process of inclusion particles was investigated by measuring the contents of inclusions in the surface, center, and bottom layers of the molten metal. In the results, main inclusions observed and determined by Prefil and PoDFA methods are MgO, Al₂O₃, spinel (MgAl₂O₄), and TiB₂ particles or thin films. It is found that some small particles of Al₂O₃ and MgO are transformed into spinel particles, and the formation rate increases as the temperature and the holding period of melt increase. The content of inclusions increases from 3.37 mm²·kg^-1 to 7.54 mm²·kg^-1 and then decreases to 3.08 mm²·kg^-1 after holding for 90 min. This is attributed to a settling phenomenon and a significant increase in settling velocity after holding for 60 min. The content of inclusion particles decreases by means of settlement and flotation in liquid aluminum with an increase in holding time. The theoretical analysis and experiment results are in essential agreement with those from industrial production.