A new HPLC method to determine related substances in risperidone by DAD and peak purity anal. was established, using C18 column (Kromasil, C18, 5 μm, 4.6 × 200 mm), acetonitrile-1% triethylamine buffer (30:70) (adjust pH to 3.0 by phosphoric acid) as mobile phase.The flow rate is 0.8 mL/min, the column oven temperature is 30°, and the detection wavelength is 260 nm.Risperidone and related substances are well separated, and the LOD of raw material 1, intermediate 1, and intermediate 2 was 0.4, 4, 0.4, and 0.6 ng.DAD and peak purity anal. are useful for evaluation of determination of related substances in risperidone by HPLC, and the method is simple, fast, specific and sensitive.