The iodine content in liquid milk was determined via gas chromatography (GC). Through systematic screening and optimization of derivatizing reagents and derivatization time, higher measured values of the iodine content in liquid milk were obtained while solving the problem of poor repeatability of the traditional method. The optimized method was more efficient than the national standard method National food safety standard-determination of iodine in food (GB 5009.267-2020). The optimal pretreatment conditions were determined to be 1.0 mL of sulfuric acid, 2.0 mL of butanone, 0.5 mL of 3.5% (V/V) hydrogen peroxide, and derivatization reaction for 30 min. This study provides a reliable basis for this optimized scheme to achieve efficient and accurate detection of iodine in liquid milk and holds significant application value in the control of the iodine content in liquid milk.