The invention provides a preparation method of lithium fluoride, which comprises the following steps: (1) introducing carbon dioxide into water, then adding the raw material lithium carbonate to obtain a lithium bicarbonate solution, then adding a precipitant, introducing carbon dioxide until the pH of the solution is 8-9, filtering, and collecting the lithium bicarbonate solution; and (2) adding hydrofluoric acid to the filtrate obtained in the step (1), carrying out fluoridation, then adding a lithium hydroxide solution, regulating the pH of the system to be 7-7.5, then filtering, collecting the filter cake, and drying to obtain the product lithium fluoride. In the invention, the industrial grade lithium carbonate is used, the total yield of the technical process achieves more than 97%, the purity is as high as 99.9% or above, and the impurity content in the product is as low as 80PPm or below.