Abstract: Objective To establish the reference ranges of thyroid stimulating hormone(TSH),free thyroid hormone(FT₄) and three free triiodothyronine(FT₃) in different gestation periods. Methods This study was based at the Hospital affiliated to Ningbo University School of Medicine.A total valid of 281 pregnant women who visited the hospital between January,2014 and December,2015 were recruited in this study according to the National Academy of Clinical Biochemistry(NACB) criteria.Blood samples were sequentially collected from the women at the first(T1,9-12 weeks),the second(T2,16-24 weeks) and the third (T3,32-36 weeks)trimesters to determine the serum FT₃,FT₄ and TSH levels using Beckman DX800 detection system,meanwhile,158 cases of non-pregnant women of childbearing age were selected as healthy controls.The percentile(P_2.5-P_97.5) was employed to indicate the reference ranges of FT₃,FT₄ and TSH in different periods of pregnancy. Results TSH reference ranges were T1:0.05-3.97 mIU/L,T2:0.12-4.28 mIU/L,T3:0.30-6.01 mIU/L,control:0.08-3.81 mIU/L respectively,FT₃ reference ranges were T1:3.33-5.78 pmol/L,T2:3.10-5.23 pmol/L,T3:2.83-4.99 pmol/L,control:3.90-5.54 pmol/L respectively,FT4 reference ranges were T1:7.25-15.52 pmol/L,T2:6.88-13.27 pmol/L,T3:5.31-10.79 pmol/L,control:6.46-14.17 pmol/L respectively;the results between different pregnant periods and control were statistically significant differences in different periods (FT₃:F=76.431,P<0.01;FT₄:F=116.753,P<0.01;TSH:F=53.670,P<0.01). Conclusion The thyroid hormone levels between pregnant women and in non-pregnant women are different significantly,moreover,the results among different periods during pregnancy are not the same at all,it is significant and necessary to establish the according reference intervals of various thyroid hormones for each pregnant period in Ningbo city.