【Objective】The present study aimed to evaluate the correlation between thyroid function in the first trimester and gestational diabetes mellitus（GDM） .【Methods】A total of 2112 singleton pregnant women had been recruited from the Third Affiliated Hospital of SunYat-Sen University during June 2016 to June 2017. Levels of free thyroxine （FT4），thyroid stimulating hormone（TSH）and thyroid peroxidase antibody（TPOAb）were measured at 9-13+6 gestational weeks. Oral glucose tolerance test（OGTT）was performed at 24-28 gestational weeks and the women were divided into GDM group（n＝224）and non-GDM group（n＝1888）. The differences of thyroid functions were compared between the two groups. Spearman was used to analyse the correlations between the thyroid hormone levels and the blood glucose levels of OGTT.【Results】There were no statistical differences in TSH［1.04（0.61-1.61）vs 1.11（0.59-1.77）μU/mL，P＝ 0.292］and FT4［16.22（14.22-18.31）vs 16.62（14.54-18.79）pmol/L，P＝0.087］between the two groups. The incidences of thyroiddys functions were also not different between the two groups（P>0.05）. No correlations were found between TSH，FT4 and the blood glucoses of OGTT after adjusting the maternalage，parity and pregestational bodymassindex.【Conclusion】There was no significant correlation between thyroid function in the first trimester and GDM.