Abstract: Rapid aggregation of iron droplets in slag to form molten pool is an important process for energy-saving ironmaking and steelmaking. Iron droplets come into contact with each other and aggregate to form a “liquid bridge” under the action of slag and iron,and appear in the form of spheroid.The factors influencing aggregation and growth of iron droplet were investigated via high temperature testing and numerical simulation. The results showed that the driving force of iron droplet aggregation in slag was the interfacial tension between slag and iron,and the aggregation of iron droplets could be accelerated by the increase in the temperature and the reducion in the viscosity of slag. As the viscosity of slag decreased from 0. 40 to 0. 15 Pa·s,the size of iron droplets increased from 94 to 3 550 μm,and the aggregation efficiency of iron droplets increased by 117%. The simulative results of variation in the diameter of iron droplets were consistent with the results of high temperature test.