Foaming slags at the top at the beginning of deslaggging, in the lower portion at the end of deslagging, and at the bottom after deslagging were taken with a sample scoop at the end of dephosphorization in the converter slag-remaining and double-slag process. The distribution characteristic of bubbles was analyzed by the macroµ analysis technique. The results indicate that the order of average equivalent diameter of bubbles is the slag at the top > slag in the lower > slag at the bottom, and the order of gas porosity is the slag at the top > slag in the lower > slag at the bottom. The formation process of foaming slags was observed and analyzed. Bubbles collide and coalesce with CO/CO2 moving into the slag. Bubbles in the upper are elevated by bubbles in the lower and the bubbles rises up with buoyancy. The drainage of liquid slag occurs with gravity and the topological structure of bubbles chan-ges. With bubble collision and coalescence, the foaming slag with larger bubbles and higher porosity in the upper and that with smaller bubbles and lower porosity in the lower are formed.