Conducted a hydraulic model experiment on 120 t top-bottom combined blowing converter. Studied the impacts of lance height and top gas flowrate on the mixing time, the penetrating depth and cavity diameter under the top blowing condition and the impacts of bottom gas flowrate, bath depth and bottom tuyeres layout on the mixing time in the bottom blowing condition. Researched the optimal factor and level under the top-bottom combined blowing condition. The results show that: In top blowing conditions, 1 000 mm is the best lance height to get the shortest mixing time; In bottom blowing conditions, 750 Nm3/h is the best bottom gas flow rate and get the shortest mixing time, the bottom tuyeres layout is of great influence on mixing time, but not the more the better; In the condition of top-bottom combined blowing, the bottom gas flowrate has the greatest influence on mixing time, and the lance height have the smallest influence on mixing time. And the bath mixing result is optimal when the nozzle holes are in a symmetric distribution line, the top gas flowrate is 10 000 Nm3/h, the bottom gas flowrate is 600 Nm3/h, the lance height is 800 mm and bath depth is 800 mm.