To address the need for iodine quantification in infant formula food for special medical purposes, a reference material for iodine analysis was developed. Powered infant formula milk for special medical purposes (containing partially hydrolyzed milk protein) was used as the matrix and added with dietary supplement of potassium iodide initially diluted with whey protein powder to establish a stable preparation system using stepwise dry dilution. The homogeneity and stability of the prepared reference material were verified using alkaline extraction combined with inductively coupled plasma mass spectrometry, and characteristic value assignment was conducted through a multi-laboratory collaborative approach. Results demonstrated excellent homogeneity and stability of the material, showing a characteristic value for iodine of (67.8 ± 4.6) μg/100 g (k = 2). This reference material could be useful for method validation, laboratory quality control, and instrument calibration for iodine determination in infant formula food for special medical purposes, providing technical support for ensuring accurate measurement of iodine content in this specialized food product.