Objective：This study aims to investigate the variations of urinary iodine concentration(UIC)and urinary creatinine (UCr)in the second and third trimester of pregnancy in Nanjing establish the reference range of UIC/UCr，in order to explore the relationship between UIC/UCr and different degrees of hypothyroidism，and study the feasibility of using UIC/UCr to assess the iodine nutritional status in pregnant women. Methods：A total of 301 pregnant women at 20~28 weeks of gestation in the First Affiliated Hospital of Nanjing Medical University from 2018 to 2020 were recruited，and their thyroid stimulating hormone(TSH)，free triiodothyroxine(FT3)，free thyroxine(FT4)，anti-thyroglobulin antibody(TgAb)，anti-thyroperoxidase antibody(TPOAb)，and anti- thyroxine receptor antibody(TRAb)were detected. UIC and UCr were measured in morning urine. The normal reference range for UIC/ UCr was determined in 137 pregnant women with normal thyroid function and antibody. The iodine nutritional status of pregnant women with hypothyroidism of different degrees was analyzed. Results：①The UIC/UCr reference interval was 106.14~269.75 μg/g in middle and late pregnancy. ②According to our UIC/UCr reference interval，iodine deficiency accounted for 22.59%，iodine adequacy accounted for 48.17%，and iodine excess accounted for 29.24%. ③FT4 decreased with the increase of UIC/UCr，and TSH increased significantly when UIC/UCr exceeded the limit. ④ The proportions of iodine excess in subclinical hypothyroidism and isolated hypothyroxinemia were higher than that of iodine deficiency. Conclusion：Using UIC/UCr instead of UIC to evaluate iodine nutritional status during pregnancy，the iodine deficiency proportion is significantly reduced. UIC/UCr is correlated with TSH and FT4. Iodine should be supplemented carefully according to the UIC/UCr value in subclinical hypothyroidism and isolated hypothyroxinemia.