The invention provides a preparation method of a battery grade lithium chloride, comprising: (1) calcium chloride is added into the acid clinker extracting solution of lithium concentrate - lithium sulfate solution, the PH value of the solution is regulated by NaOH to eliminate Fe and Mg, and the precipitation of CaSO4.2H2O, Fe(OH)3 and Mg(OH)2 and lithium chloride solution are obtained after the reaction; (2) the products of step (1) are filtered and cleaned to eliminate the precipitation of CaSO4.2H2O, Fe(OH)3 and Mg(OH)2, and the LiCl solution, i.e. a conversion solution is prepared; (3) the conversion solution is added with BaCO3, and filtered and cleaned after the reaction, to eliminate SO42- and Ca2+, and the LiCl concentrate liquid 1 is prepared; (4) the LiCl concentrate liquid is added with HCL and boiled to eliminate CO32-, and added with NaOH solution to back blend PH, then be evaporated, condensed, cooled, crystallized and separated, and the LiCl concentrate liquid 2 is obtained; (5) the LiCl concentrate liquid is added with refining agent, and filtered and cleaned after the reaction to eliminate Na, and the LiCl finish liquid is prepared, the LiCl finish liquid is condensed and dried, and finally the battery grade LiCl product is prepared. The invention has simple production process and can be easily operated.