Abstract: By hydrodynamic model experiments, the effect of topblown gas, bottom blown gas and CO gas on bath stirring in 150 t top-bottom converter were studicdt According to method of orthogonal experiment design, the essetial factors and optimal amount of top and bottom gas were found. At high carbon range, compared with the stirring by CO, the stirring by top and bottom blown gas could be neglected; at low carbon range, the stirring by bottom blown gas was the main factor. The optimal gas amound was about 5 Nm³/h. The equations of mixture time and rate constant of mass transfer were established.