The invention discloses a salt (I) of a 3-amino-2-propanol acetamide compound, and also discloses a preparation method of the salt, and use of the salt as a reference substance or a standard substance of related substance in quality control of a linezolid preparation. In a formula, A represents boric acid, phosphoric acid, C1-8 fatty acid, trifluoroacetic acid, benzoic acid, salicylic acid, phthalic acid, mandelic acid, oxalic acid, maleic acid, fumaric acid, succinic acid, tartaric acid, citric acid, methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, and p-toluenesulfonic acid; n represents 1/2 or 1; the compound is a racemate, an (S)-optical isomer or an (R)-optical isomer.