A method for purifying a salt of reduced form of β-nicotinamide adenine dinucleotide (NADH) includes: sequentially microfiltrating and nanofiltrating a reaction solution obtained after an enzymatic reaction, collecting a concentrate for use; adding an ion pair reagent to the concentrate, and purifying by gradient elution to obtain a purified filtrate using a reverse-phase chromatographic column as a stationary phase, a buffer solution as a phase A, and ethanol as a phase B; changing the cations in the purified filtrate into sodium ions to obtain a filtrate by using a cation exchange resin; and nanofiltrating the filtrate, and freeze drying in a vacuum freeze drier. The method results in an excellent purity and yield of a salt of NADH that meets requirements in industry.