【Abstract】 Objective To observe the efficacy of levothyroxine sodium tablets in the treatment of pregnant women with subclinical hypothyroidism (SCH) of negative thyroid antibodies during pregnancy and its effects on pregnancy outcomes. Methods The data of pregnant women with pregnancy and SCH of negative thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb) in the Department of Obstetrics and Gynecology of Qionglai Medical Center Hospital from July 2016 to July 2018 were retrospectively analyzed. 50 pregnant women with levothyroxine sodium tablets after diagnosis and 50 pregnant women without treatment after diagnosis were randomly selected and included in SCH treated group and SCH untreated group. The data of another 50 normal healthy pregnant women examined at the same time in our hospital were listed as healthy control group. The levels of serum folic acid and related indicators of thyroid function ［serum thyroid stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4)］were compared before treatment and after 4 w of treatment between SCH treated group and healthy control group. The pregnancy outcomes of pregnant women (shun yield, incidence rates of premature birth, abortion, intrauterine distress and fetal malformation), neonatal thyroid function indicators (TSH, FT3, FT4) and height, weight and 1min neonatal Apgar score were analyzed among the three groups. Results After 4 w of treatment, serum folic acid level in SCH treated group was significantly higher than that before treatment (all P＜005), but was lower than that in healthy control group (all P＜005). The serum TSH was significantly lower than that before treatment (P＜005), but was higher than that in healthy control group (P＜005). There were no significant differences in the serum FT3 and FT4 compared with the same group before treatment and healthy control group (all P＞005). The shun yield and neonatal weight in SCH treated group were significantly higher than those in SCH untreated group (all P＜005), and the incidence rates of premature birth and abortion and the serum TSH level were significantly lower than those in SCH untreated group (all P＜005), and there were no significant differences in the indexes compared with those in healthy control group (all P＞005). There were no significant differences in the incidence rates of intrauterine distress and fetal malformation, neonatal height, Apgar score and serum FT3 and FT4 levels (all P＞005). Conclusions Levothyroxine sodium tablets for patients with SCH during pregnancy can regulate the thyroid function of pregnant women and improve the pregnancy outcomes, and it is conducive to the healthy growth and development of fetuses.