To investigate relationship between serum 25-hydroxyvitamin D (25-OH-VD) level and hypothyroidism of pregnant women with ≤12 gestational weeks. Methods: 90 early pregnancy women who underwent prenatal examination were enrolled in this study from August 2015 to August 2018. The levels of serum 25-OH-VD, free thyroxine (FT4), thyroid peroxidase antibody (TPOAb), thyroid stimulating hormone (TSH), and triiodothyronine (FT3) of these women were measured. The correlation between vitamin D level and thyroid function indexes of these women, and the influence of vitamin D level on their thyroid function were analyzed. Results: The serum 25-OH-VD level of these 90 women was 16.74±4.27 μg/L (5.16 to 43.86 μg/L). The proportion of women with vitamin D deficiency, with vitamin D insufficient, and with vitamin D adequation had accounted for 66.7%, 23.3% and 10.0%, respectively. There were no significant differences in serum FT4, TSH or FT3 levels among the women with vitamin D deficiency, with vitamin D insufficient, and with vitamin D adequation (P>0.05). TPOAb level of the women with vitamin D deficiency, insufficient and adequation was decreased gradually (P<0.05). There was no significant difference in proportion of the women with normal thyroid function or hypothyroidism among the women with different vitamin D levels (P>0.05). There was no significant difference in proportion of the women with hypothyroidism, subclinical hypothyroidism or low T4 among the women with different vitamin D levels (all P>0.05). Serum 25-OH-VD level of the women was not correlated with their levels of FT4, TSH or FT3 (P>0.05), which was negatively correlated with the TPOAb level (P<0.05). Multivariate Logistic regression analysis showed that the levels of FT4, TSH and FT3 of the women had not affect their vitamin D level (P>0.05), but the increased TPOAb level of pregnant women had improved their risk of vitamin D deficiency (P<0.05). Conclusion: There is vitamin D deficiency in some early pregnant women. There is no correlation between serum 25-OH-VD level of pregnant women and their hypothyroidism, however, the increased TPOAb level will increase the risk of vitamin D deficiency of pregnant women.