Objective To establish the thyroid hormone reference range for healthy pregnant women during different pregnancy period and to provide reference for the diagnosis, treatment, monitoring of maternal thyroid disease. Methods The thyroid hormone levels in healthy pregnant women including 137 cases of early pregnancy, 147 cases of second trimester pregnancy, 139 cases of late pregnant and 130 cases of non pregnant women were determined. Results The TSH level in early pregnancy wonmen was significantly lower than that of non pregnant women (P<0.01), and it increased gradually as the process of pregnancy, but still lower than that of non pregnant women. The serum TT4 and TT3 levels were increased from early pregnancy and reached the highest levels at the second trimesterpregnant (P<0.01). The serum FT4 and FT3 levels in second trimester and late pregnancy were significantly lower than that of non pregnant women (P<0.01). Conclusion The thyroid hormone levels in pregnant women and non pregnant women are different. There are obvious differences between each pregnancy period.The establishment of reference range of thyroid hormone during pregnancy could provide the clinical value for diagnosis and treatment of thyroid disease in pregnancy wonmen.