The effect of LF refining slag and Ca content on the nozzle clogging was focused on the basis of analysis of blockage and combined with the actual production of 20CrMnTiH. The results show that, through the optimization and adjustment of Al 2 O 3 and MgO fractions in refining slag, controlling the molten steel Ca content in 15×10 -6 ~ 25×10 -6 can prevent nozzle clogging effectively and raise the molten steel castability.