The invention discloses a method for preparing lithium fluorosulfonate by using an organometallic lithium reagent, which comprises the following steps: (1) slowly mixing and reacting the organometallic lithium reagent serving as a lithium source with fluorosulfonic acid under a low-temperature condition in the presence of perfluorohexane serving as a solvent to obtain a lithium fluorosulfonate crude product; and washing the crude product with a reaction solvent for 5 times; (2) carrying out vacuum pumping on the crude product, adding a poor organic solvent of lithium fluorosulfonate, washing for three times, and carrying out vacuum pumping on the poor organic solvent to obtain a solid; (3) adding carbonate, nitrile and alcohol organic solvents into the solid, extracting, filtering, concentrating, adding a low-polarity aprotic solvent into the concentrated solution, and carrying out static crystallization; and (4) filtering the crystals again, and carrying out vacuum drying to obtain the lithium fluorosulfonate product. The preparation steps are carried out without water under the protection of inert gas. According to the preparation method provided by the invention, the lithium fluorosulfonate can be prepared, the yield is high, the product quality is stable, and the content of impurities such as potassium ions, sodium ions, calcium ions, fluorine ions, sulfate ions and water in the product can be effectively reduced.