Abstract: 1 ： 2 water hydraulic model is established based on similar theory for a 1 500 mm x 230 mm slab mold as a prototype at a steelworks. The results show that when the blowing gas flowrate is certain, the fluctuation of die liquid level from the center of the nozzle to the narrow side first increases and then decreases, and when the blowing gas flowrate is more than 0. 8 L/min, the phenomenon of slag entrapment begins to occur and the number of bubbles in the mold becomes more. The increase of immersion depth makes the liquid level fluctuation weaker, and the effect of immersion depth in the range of 65 ~ 95 mm on the effect of slag entrapment is not significant. Increasing casting speed increases the impact depth of the flow strand, with large slag droplets being involved at casting speeds more than 1. 1 m/min. When the casting speed of the mold is 1.0 ~ 1.1 m/min, the blowing gas flowrate is 0. 6 ~0. 8 L/min, and the immersion depth is 75 ~ 85 mm is more reasonable. The production practice of C45E steel shows that as the drawing speed is adjusted from 0. 9 ~ 1.2 m/min to 1.0 ~ 1. 1 m/min and the immersion depth is improved from 130 ~ 190 mm to 150 ~ 170 mm, the billet defect rate is reduced from 6% to 1.9%.