The invention discloses a trifluoromethanesulfinic acid purification method. The method comprises the following steps: mixing and stirring a sodium trifluoromethanesulfinate industrial product, anhydrous magnesium sulfate and a solvent, carrying out suction filtration while stirring, collecting the filtrate, putting a filter cake in an original stirred reaction kettle, further adding the solvent, carrying out suction filtration while stirring, collecting the filtrate, collecting all the filtrates and filtrate solutions after leaching and putting all the filtrates and filtrate solutions after leaching in the kettle, carrying out reduced-pressure drying, recovering the solvent, adding deionized water to obtain a sodium trifluoromethanesulfinate water solution; then sending the sodium trifluoromethanesulfinate water solution to a dryer for spray drying, thus obtaining the sodium trifluoromethanesulfinate powder product with content of 95% or above. The method has the beneficial effects that high content sodium trifluoromethanesulfinate is extracted from the sodium trifluoromethanesulfinate industrial product by using the solvent and high content sodium trifluoromethanesulfinate without inorganic salts, such as bromide ions, is obtained after the solvent is removed, thus meeting the production requirements of lithium ion battery electrolyte bis(trifluoromethane)sulfonimide lithium salt.