Objective To develop a high-performance liquid chromatography (HPLC)-diode array detector (DAD) method for determination of 20 colorants in hair dyes, so as to improve the method for determining oxidative hair dyes in Hygienic Standard for Cosmetics. Methods After ultrasonic extraction with ethanol-water, samples were analyzed by HPLC. The separation was achieved on an Agilent Zorbax Bonus-RP column (4.6 mm×250 mm,5 μm) using a gradient mobile phase system of A: acetonitrile and B: 4 mmol/L PBS (pH=6.0) containing 0.1% 1-octanesulfonic acid sodium salt solution at a flow rate of 1 mL/min. The gradient elution program was as follows: 0-24 min, 10% A; 24-26 min,10%-40% A; 26-45 min,40% A; 45-47 min,40%-80% A; 47-52 min,keep 80% A unchanged. The detection wavelength was set at 280 nm,the temperature of column was 15℃, and the injection volume was 5 μL. Results All the components were separated at baseline within 50 min. Within the concentration range of 10.0-500.0 mg/L, the peak areas and concentrations of colorants had good linear relationship, with the linear correlation coefficients being higher than 0.999. The intra-day and inter-day precisions were within 4% and the average recoveries ranged from 81.90% to 119.88%. Conclusion The present method is simple, rapid and accurate and is suitable for determination of colorants in oxidative hair dyes.