During oxygen steelmaking process, a systematical description of the interaction behaviour between top blown jet and molten steel is extremely important. In the present study, a cold model experiment and the corresponding numerical simulation were carried out to illustrate the highly complex interaction process inside an 80-t converter. First, the interaction process was presented in a numerical way. On this basis, the quantitative effect of pertinent operational parameters on the interaction process was investigated. To clearly describe the cavity appearance, the cavity shape index ( ) was put forward, which is a dimensionless factor to demonstrate the cavity shape related to cavity depth and cavity width. In addition, a functional relationship correlating cavity shape index and blowing number was proposed. It can be concluded that higher blowing number (N_B) results in deeper cavity depth and smaller cavity width. Moreover, the effect of cavity shape on the stirring characteristics and the mixing effect in the converter were investigated. The results show that lower and higher cavity shape index may lead to longer mixing time in smelting process. For 80-t converter, the penetration depth and impact width should be controlled approximately equal ( fluctuates around 1) to obtain better mixing effect.