Abstract: Orthogonal experiment with 4 factors and 5 levels by using 120 t BOF geometric similarity 1：7 water model has been earned out to study the effect of height of oxygen lance from pool (200 -280 mm) , top lance flow rate (72. 5 ~ 99. 0 m³/h) , bottom blowing flow rate (0. 8 ~2. 4 m³/h) and distribution of bottom blowing holes (4 ~ 8 holes) position on BOF top and bottom combined blowing. Results show that distribution of bottom blowing holes position is most important factor to influence the mixing effect of liquid pool, with height of oxygen lance from pool h = 240 mm, top lance flow rate Q₁=99. 0 m³/h, bottom blowing flow rate Q₂=2. 4 m³/h and 6 holes bottom blowing position D)(4) , the mixing effect of liquid pool is best. The results of steel Q235B production application of 120 t BOF top and bottom combined blown obtain that with top blowing rate 25 000 m³/h, bottom blowing rate 560 ~ 800 m³/h and bottom blowing by 6 holes distribution the liquid end [ C] is 0. 14% 〜0. 18% and the carbon oxygen product is 0.002 3 ~0.002 5 by blowing for 14 ~ 16 min to get better pool mix effect.