In order to solve the bottleneck problems of"zero balance displacement"and"large variation of breastmilk"in the study of iodine EAR of pregnant women, lactating women and infants, firstly, this study intends to clarify the rate of metabolism and distribution of iodine during pregnancy by 125I tracer, SPECT/CT in vivo small animal imaging and γ counting study. Then, the iodine balance study in rats was conducted to verify the degree of "zero balance value displacement"caused by the difference of iodine absorption and store in different organs and tissues under different iodine exposure levels, so as to determine the iodine selection conditions of subjects in the population experiment. To determine the EAR of pregnant women by optimizing the population iodine balance experiment. Secondly, we proposed to study the regulatory mechanism of NIS and Pendrin in the mammary gland of lactating rats under different iodine nutrition levels to clarify the range of breastmilk iodine compensation. Mammary cell experiments intend to clarify the mutual regulations of iodine nutrition, oestrogen, and NIS and Pendrin. Based on the results of animal and cellular experiments, and the effect of genetic, oestrogen and iodine status were considered, a cross-sectional study of lactating women was conducted to determine the normal reference range of breastmilk iodine after screening out the people with abnormal indicators. This study will solve the bottleneck problems and difficulties in the iodine RNI research for pregnant women, lactating women and infants, found the iodine nutritional compensatory mechanism under special physiology, and provide the scientific basis for obtaining the accurate EAR basic data and the revision of iodine DRIs.