Abstract: In view of the serious tundish nozzle clogging and less casting sequences in casting SPHD low-carbon low-silicon Alkilled steel that produced by LD-RH-CC process in a factory,the effects of adding the fluorite into the RH slag on the inclusions and castability of SPHD steel were studied. The results show that the main component of the blockage is Al₂O₃ -CaO-MgO with more than 70% of Al₂O₃ mass fraction. The mass fraction ratio of CaO to Al₂O₃ in refining slag can be controlled at 2 by adding some block fluorite through the vacuum chamber of RH furnace which is benefit to lower the content of Al₂O₃ in the slab and also reduces its particle size. Furthermore,the proportion of CaO·Al₂O₃ inclusions is increased and the average continuous casting heats can be raised to 3 at least.