The JN series of Composite Desulphurizer is applied to the KR and a dusting hot metal desulphurization process. The qualified rate of primary desulfurization of low-silicon molten iron is over 95%, the trace of sulfur after the treatment of ultra-low-sulfur molten iron reaches more than 90%, and the rate of no trace after heavy removal is more than 80%. The molten steel desulfurizer is suitable for synthetic slag washing, out-of-furnace refining and desulfurization processes, and the first-time desulfurization pass rate is over 70%.