Objective To explore the effect of subclinical thyroid function in pregnancy loss (SCH) complicated with gestational diabetes mellitus (GDM) during pregnancy complications on pregnancy outcome. Methods 140 cases of pregnancy complicated with SCH and 122 cases of normal thyroid function of pregnant women were selected for routine screening of gestational diabetes mellitus. The patients were then divided into SCH with GDM group, SCH group, GDM group, normal group. The outcome of 4 groups of pregnant women during pregnancy were observed and recorded. Results The rate of spontaneous abortion and the incidence of diabetes in pregnancy with SCH group were significantly higher than that of normal thyroid function group. The fetal growth restriction, oligohydramnios, premature delivery of SCH combined with GDM group was significantly higher than that in normal thyroid function group, and the outcome of pregnancy in fetal distress and caesarean section and the incidence of neonatal asphyxia were obviously higher than that in normal thyroid function group (P<0.05). Conclusion The subclinical hypothyroidism with gestational diabetes mellitus in pregnancy women during pregnancy may have great harmful on mothers and infants, and should be screening early for treatment.