An analytical method using high performance liquid chromatography (HPLC) for separation and quantitative determination 9 kinds of byproducts degraded by 60Co γ irradiation on Miscanthus was developed. The separation was carried out on a C18 column with the following conditions: the mobile phase of acetonitrile and 0.01mol (NH4)2HPO4 (phosphate adjust to pH=2.7), 25 ℃ of column temperature, flow rate of 0.8 mL/min and multi wavelength detection. The result showed that the byproducts of Miscanthus degraded from 60Co γ irradiation were well separated and their contents were well determined with relative standard deviations from 1.5% to 2.3%, and detection limits varied from 0.10 to 0.89 mg/L. Water extracts of Miscanthus irradiated with 1 200 kGy 60Co γ were detected using the methods at above condition, it was found that the target chemicals in water extracts were included in p–hydroxybenzoic acid, vanillic acid, syringic acid, 4–hydroxybenza ldehyde, vanillin, p–coumaric acid, furfural, formic acid, and acetic acid, and their contents was 17.78 mg/L, 12.43 mg/L, 3.26 mg/L, 15.40 mg/L, 10.18 mg/L, 16.42 mg/L, 2.52 mg/L, 102.29 mg/L, and 86.24 mg/L, respectively. It was proved that the method was applicable to quantitative determination the main degradation byproducts of Miscanthus with 60Co γ radiation pretreatment.