Objective: To establish and analyze the reference range of serum thyroid hormone levels in pregnant women in Zhangzhou, and to provide basis for pregnancy examination and subsequent research. Methods: A total of 983 pregnant women with normal antenatal examination in Zhangzhou Hospital from December 2019 to May 2021 were selected as the research objects, including 269 cases in the early pregnancy, 400 cases in the middle pregnancy and 314 cases in the late pregnancy. At the same time, 368 serum samples of healthy non-pregnant women were taken as the non-pregnant control group. The contents of FT3, FT4 and TSH were determined by chemiluminescence immunoassay, and the changes and the range of normal reference values were statistically analyzed. Results: With the development of pregnancy, the serum FT3 and FT4 of pregnant women showed a gradual downward trend. There was no significant difference in FT3 and FT4 levels between the early pregnancy and the non-pregnant control group, respectively, while the middle pregnancy and late pregnancy were significantly lower than those of the non-pregnant control group (P＜0.05), and the differences among the three groups during pregnancy were statistically significant (P＜0.05). The level of TSH was significantly decreased in the early and middle pregnancy, and was the lowest in the early pregnancy. After that, it gradually increased with the development of pregnancy, and was close to the non-pregnant control group in the late pregnancy (P>0.05). In non-pregnant control group, early pregnancy group, middle pregnancy group and late pregnancy group, the reference ranges of serum FT3 were 3.96-6.16, 4.08-6.20, 3.51-5.86, 3.57-5.53 pmol/L, respectively; the reference ranges of serum FT4 were 8.15-13.59, 8.04-13.34, 6.46-11.60, 6.16-10.66 pmol/L, respectively; the reference values of TSH were 0.58-4.73 mIU/L, 0.33-4.18 mIU/L, 0.33-3.96 mIU/L and 0.47-4.06 mIU/L, respectively. Conclusion: The serum thyroid hormone levels of pregnant women in pregnancy have changed, and the reference ranges of specific thyroid hormone levels in different pregnancy periods in this region are preliminarily established for routine screening of normal pregnancy and subsequent studies.