Objective To investigate the effect of levothyroxine tablets on subclinical hypothyroidism in pregnancy.Methods One hundred and twenty patients with the subclinical hypothyroidism in hospital were divided into four groups,subclinical hypothyroidism + TPOAb (+) treatment group (39 cases),subclinical hypothyroidism + TPOAb(+) untreated group (15 cases),subclinical hypothyroidism + TPOAb (-) treatment group(26 cases) and subclinical hypothyroidism + TPOAb (-) untreated group (40 cases).Patients in the treatment groups were administrated with levothyroxine tablets.Results The levels of thyroid stimulating hormone(TSH) in subclinical hypothyroidism and TPOAb(+) treatment group were significantly lower(16-20 weeks and 28-32 weeks) at after treatment,which was also lower than that in B group(t =5.671,6.661,P ＜ 0.001).Compared with the untreated group,there was a significant difference in terms of average gestational age,fetal weight ((39.3 ± 1.6) weeks vs.(37.9 ± 1.4) weeks ; (3524 ± 562) g vs.(3101 ± 351) g,t =4.561,7.834,P ＜ 0.001) between A and B groups.In B group,premature birth,gestational hypertension,incidence of placental abruption were significantly higher than that in A group (26.67％ and 2.56％,x2 =7.490,P ＜ 0.001 ; 5.13％ and 40.00％,x2 =10.438,P ＜ 0.001 ; 0 and 13.33％,x2 =5.400,P =0.020).In C group after 16 weeks of treatment,TSH levels at (16-20) weeks and (28-32) weeks were significantly decreased.Compared with the D group,the differences were statistically significant (t =4.980 and 5.432,both P ＜ 0.001).There was no significant difference in C group and D group in terms of pregnancy outcome (P ＞ 0.05).Conclusion Patients with gestational subclinical hypothyroidism such as mergers TPOAb(+) should be treated in time.Prompt treatment can significantly reduce the incidence of adverse pregnancy outcomes,but if patient with TPOAb(-),It is recommended not to conduct any treatment.