The effect of VOD bottom blowing location and blowing rate on mixing time of molten steel was studied by a water model corresponding to 1/9 volume of the 75 t ladle with oval cross section at Taiyuan Steel.The test results showed that the available blowing rate for model was 1.1~1.3 m³/h coresponding to flowing rate 350~460 L/min in VOD refining of 75 t molten steel; the location of single blowing brick at bottom was nearer to ladle center the mixing time was shorter; and the mixing time was obviously shorter as bottom blowing with 2 or 3 blowing bricks but there were optimum distribution locations af bottom bricks. There were optimurn matching of top blowing rate and bottom blowing rate and coresponding location during top-bottom blowing to get better effect.