A gas chromatographic method for determining the iodine content in milk powder was established, and the homogeneity and stability of iodine reference material were evaluated. Butanone derivative with iodine produced under acidic conditions was detected by gas chromatography (GC) with an electron capture detector and quantified by an external standard method. The proposed method showed a good linear relationship (R² = 0.9996), the recoveries from spiled samples were between 95.3% and 101.3%, and the relative standard deviation (RSD) was 2.3% (n = 6). This method had high accuracy and could be used for the determination of the iodine content in milk powder.