The invention discloses a special-purpose high-precision high-performance liquid chromatography method for detecting gamma-aminobutyric acid and sixteen amino acids hydrolyzed from protein in a milk-including drink at the same time. The method comprises three operation steps of sample hydrolysis, derivatization processing, and on-column detection. Processing reagents used in the three operation steps, reagent consumption, and processing parameters are set according to characteristics of the milk-including drink, so that technical parameters of the three operation steps closely match each other, and gamma-aminobutyric acid and sixteen amino acids hydrolyzed from protein in the milk-including drink can be detected with high precision in one step. Through the method, one-step detection of gamma-aminobutyric acid and sixteen amino acids hydrolyzed from protein in the milk-including drink is achieved, and the method has extremely high sensitivity and excellent stability.