Hainanmycin sodium is a new type of monobasic acid polyether antibiotics, which has been widely used in chicken, cattle and sheep and other animal feeds, and it is mainly used to prevent coccidiosis and regulate growth metabolism. The color reaction between hainanmycin and derivative can be detected by UV spectrophotometry. The results showed that the derivatives of p-dimethylaminobenzaldehyde and vanillin had the maximum UV absorption at 595 nm and 590 nm, respectively, and hainanmycin had the lowest detection limit after vanillin derivatization. When the derivative agent was composed of 4% vanillin (g/100 mL), 20% hydrochloric acid and 80% anhydrous ethanol, the derivative reaction with hainanmycin solution was carried out at 90 ℃ for 5 min at the volume ratio of 4∶6 (V∶V), and the color effect was the best after derivatization. Hainanmycin showed a linear relationship with the absorbance in the concentration range of 5~50 μg / mL, and the R2 (Coefficient of determination) was 0.993. This method could quantify the hainanmycin content in the premix and feed. The limit of quantification was 4.8 mg/kg in feed, and the recoveries of hainanmycin in feed and premix were 74.5%~93.8% and 83.2%~101.3%, respectively. It can be used as an effective method for the detection of hainanmycin in feed and premix.