Since 1996, the compulsory universal salt iodization policy has been implemented nationwide. In the 20 years of policy implementation and revision, the iodine nutritional status of the Chinese population experienced 5 consecutive years of excess iodine, 10 years of super-sufficient iodine and 5 years of moderate iodine. In order to gain a more accurate and comprehensive understanding of the changes in the prevalence of thyroid diseases in mainland China from 2009 to 2015 with the transition from excessive iodine to moderate iodine status, this study provides data from two population-based repeated cross-sectional surveys with nationally representative surveys; Furthermore, this study determined changes in thyroid stimulating hormone levels. Both cross-sectional surveys used a multi-stratified phased random sampling approach to include participants aged 18 years and older from seven geographic regions across the country who had lived in the chosen community for at least 5 years; If female, require not to be pregnant. After excluding participants with missing information on gender, age, thyroid function, and thyroid ultrasound, a total of 14 925 participants in 2009 and 12 553 participants in 2015 were included in this study.
