An HPLC method for determination of aspartic acid in potassium magnesium aspartate injection was established.Inertsil ODS-SP column (5 μm, 4.6 mm×250 mm) was used.The mobile phase was acetonitrile-30 mmol·L-1 sodium dodecyl sulfate (plus 0.85 mL triethylamine, pH adjusted to 2.5 using phosphoric acid) (150:850) with a flow rate of 1.0 mL·min-1.The detection wavelength was 210 nm, with the column temperature of 40°C.Aspartic acid had a good linear relation in the range of (2.06-12.36) μg (r=0.9998, n=6).The average recovery (n=6) was 99.72%, and RSD was 1.0%.This method is simple, accurate and well stable, which can be used as an effective detection method of potassium magnesium injection.