【Objective】To investigate the relationship of different types of gestational diabetes mellitus（GDM）and thyroid function.【Methods】A Total of 3846 cases，which received prenatal examination，delivered in the Eastern Hospital of the First Affili? ated Hospital，Sun Yat-sen University and performed a 75 g oral glucose tolerance test（75 g 0GTT）at 24-28 gestational weeks， from Jan 1st，2014 to Dec 31st，2015，were divided into 2 groups. Normal blood glucose group：the result of OGTT（fasting plasma glucose，1 hour glucose and 2 hour glucose）was normal；Gestational diabetes mellitus group（GDM group）：the result of 0GTT was abnormal. GDM group were divided into Ⅰ，Ⅱ，and Ⅲ. GDM I defined as one abnormal blood glucose of result. GDM Ⅱ：two ab? normal blood glucose. GDM Ⅲ：three abnormal blood glucose. 1868 cases of healthy pregnant women were reselected as the control group. TSH，FT4 and TPO Ab were detected in two groups. Analysis of Variance，Mann-Whitney U test，Kruskal Wallis rank test or Fisher′s test was used for statistical analysis.【Result】There were statistically significant difference in TSH，FT4 between GDM sub? group and control group（P = 0.012，P = 0.002）. TSH median trend to increase in GDM Ⅱ，and FT4 median trend to decrease inGDMⅡ. The Prevalence of hypothyroidism in GDM Ⅱ and GDM Ⅲ were higher than those in control group.【Conclusion】The GDM group with two or three abnormal blood glucose had a higher incidence thyroid gland dysfunction，especial with subclinical hypothy? roidism. We should fully test the thyroid function，treat diabetes as early as possible and improve the pregnancy outcome as we could.