The purpose of this study was to establish an HPLC method for the determination of the related substances in Cyclopentolate Hydrochloride.The chromatog. column was YMC Triart C8 (4.6×250 mm, 5μm).Mobile phase A was 0.2 mol/L ammonium phosphate with 0.1 mol/L sodium heptanesulfonate (adjusted pH=3.0 with phosphoric acid), and mobile phase B was acetonitrile with gradient elution.The flow rate was 1.0 mL/min; the detection wavelength was 220 nm; the injection volume was 20μL; the column temperature was 30°C.Based on selected condition, the resolutions between Cyclopentolate Hydrochloride peak and kown impurities A, B, C, E, H peaks were fine.Linear range of impurities A, B, C, E and Cyclopentolate Hydrochloride were 0.2171∼2.1714, 0.2046∼2.0465, 0.2151∼2.1514, 0.2022∼2.0223, 0.2068∼2.0683μg/mL, resp.LOQ of impurities A, B, C, E and Cyclopentolate Hydrochloride were 0.0832, 0.1121, 0.0593, 0.0446, 0.1017μg/mL, resp.Repeatability and recovery of this method were good.This method is specific, accurate and convenient, which applies to analyze the related substances in Cyclopentolate Hydrochloride.