A method for purifying β-nicotinamide mononucleotide (NMN) includes: sequentially microfiltrating and nanofiltrating a crude product solution containing NMN using membrane concentration devices to obtain a concentrated crude product solution; adjusting the concentrated crude product solution to pH 3-7 to obtain a loading solution, loading the loading solution onto a preparative reverse phase high performance liquid chromatographic column, and purifying by gradient elution using an octadecylsilane-bonded silica gel as a stationary phase, a hydrochloric acid solution at pH 3-7 as a mobile phase A, and 100% ethanol as a mobile phase B, to obtain a purified sample solution; concentrating the purified sample solution by nanofiltration and freeze drying in a vacuum freeze drier to obtain a purified NMN.