OBJECTIVE： To establish a method for the determination of related substance in posaconazole raw material. METHODS： HPLC method was adopted. The separation was performed on Zorbax Eclipse Plus C18 column with mobile phase consisted of 0.05 mol/L ammonium acetate solution （pH adjusted to 4.0 using acetic acid）-acetonitrile （gradient elution） at the flow rate of 1.0 mL/min. The detection wavelength was set at 262 nm， and the column temperature was 30 ℃. The sample size was 20 μL. RESULTS： The linear range of intermediateⅠwas 0.05-5.0 μg/mL （r＝0.999 9）； the limit of quantitation was 0.05 μg/mL， the limit of detection was 0.013 μg/mL； RSDs of precision test， stability test and repeatability test were lower than 2.0％； the recoveries was 98.00％-101.69％（RSD＝1.22％，n＝9）. CONCLUSIONS： The method is simple， accurate and suitable for the determination of related substance in posaconazole raw material.