The combined blowing process of metallurgical multiphase reactor was simulated by water modeling. The effects of operation conditions on dispersed phase size distribution were studied and an empirical formula was obtained. Based on the law of additive codimensions, the interface areas under different operation conditions were calculated by means of box counting and projection relationship. The results show that the frequency of dispersed phase with certain granularity level are in a certain proportion to its size level, and the dispersed phase areas are influenced by the top and bottom combined blowing.