Abstract: In order to study the slag entrapment and its influencing factors at the steel-slag interface, the hydraulic simulation experiment was carried out. This experiment broke down the slag entrapment process under the bottom blowing condition and expounded the cause and formation process of oil droplet formation. The factors affecting slag entrapment were studied by changing oil thickness and viscosity. It was found that the relationship between the critical blowing flow and cinder viscosity is approximately linear with y=0.00165x+0.72581. For the same cinder viscosity, the minimum diameter of the oil droplets gradually decreases with the increase of the blowing flow rate; while for the silicone oil of different viscosity, the maximum and minimum oil droplet diameters increase gradually with the increasing viscosity. As oil layer becomes thicker, the critical slag gas volume decreases linearly with y=1.2-0.2x.