An efficient and sensitive analytical method for the simultaneous content determination of 18 amino acids in compound amino acid injection was developed using high performance liquid chromatography (HPLC) with pre-column derivatization. Phenyl isothiocyanate (PITC) was used as derivatization reagent. The target compounds were separated on a Unitary-C18 column (250 mm í 4.6 mm, 5 μm) in gradient elution mode using sodium acetate and the mixture of acetonitrile, methanol and water as mobile phases. The detection wavelength was 254 nm. The derivatization reagent dosage, derivatization time, salt concentration, the pH and the column temperature of mobile phase were investigated. Finally, 18 amino acids were separated within 40 minutes. The method showed that the good linearity (r2 ≥ 0.997 7) was at a range from 9 μg·mL-1 to 1 021 μg·mL-1. The recoveries ranged from 92.6% to 110.7%. And the relative standard deviations (RSD) ranged from 0.01% to 5.68%. The limits of quantification (LOQ, S/N = 10) ranged from 0.02 μg·mL-1 to 13.41 μg·mL-1. This method, which was simple, sensitive and accurate, can be applied for the content determination of amino acids in compound amino acid injections.