The invention provides a method for detecting the content of impurity aldol dimer through degradation in an oxycodone liquid preparation, and belongs to the technical field of pharmaceutical analysis. According to the method, high performance liquid chromatography is adopted for detection, detection conditions are accurately controlled, octadecylsilane chemically bonded silica is selected as a chromatographic column of a filling agent, the composition and proportion of a mobile phase are controlled, a gradient elution method is adopted, a gradient elution procedure is controlled, and the content of the impurity dimer generated by degradation in the oxycodone hydrochloride liquid preparation can be detected. The detection method is high in sensitivity and specificity, it can be ensured that the genotoxic impurity dimer in the oxycodone hydrochloride liquid preparation is effectively detected, a powerful control strategy is provided for product quality control of the medicine, and a guarantee is effectively provided for product quality and safety. Moreover, the detection method disclosed by the invention is accurate, stable, durable, scientific and reliable, and the content of oxycodone aldol dimer in the oxycodone liquid preparation can be well measured.