The invention discloses a strong desulphurizer containing BaO and Li2O, a production method thereof and a method for deeply desulfurizing liquid steel. Barium carbonate, lithium carbonate or barium carbonate, lithium carbonate and boron oxide are used as raw materials, the barium carbonate and the lithium carbonate are decomposed into barium oxide and lithium oxide by utilizing the waste heat of a steel ladle and the heat of liquid steel, and then desulphurization is realized by using the barium oxide and the lithium oxide. The strong desulphurizer contains the components in percentage by mass: 50-95 percent of BaCO3, 3-25 percent of Li2CO3, or 50-95 percent of BaCO3, 3-25 percent of Li2CO3 and 5-20 percent of B2O3, and the balance of impurities and water. The barium carbonate, the lithium carbonate and the boron oxide are proportioned according to the components of the strong desulphurizer, then crushed, stirred and mixed for 15-30min and packaged into a finished product according to the requirement of weight after uniformly mixing. When the liquid steel is deeply desulfurized, a 90t ultrahigh electric arc furnace is adopted, and the production process flow is as follows: EAF-LF-VD-CC.