Objective To observe the effect of hepatitis B virus (HBV) on pregnancy outcome in patients with gestational diabetes mellitus (GDM). Methods 160 patients with GDM treated in our hospital from October 2019 to April 2021 were included as the research objects, and a retrospective analysis was carried out. According to the existence of HBV infection, all patients were divided into observation group (group A, 96 cases of GDM combined with HBV infection) and control group (group B, 64 cases of simple GDM). The observation group (group A) was divided into abnormal liver function group (group A1, 42 persons) and normal liver function group (group A2, 54 persons) according to whether there was abnormal liver function during pregnancy. The use rate of insulin during pregnancy, the incidence of pregnancy induced hypertension (HDCP), intrahepatic cholestasis of pregnancy (ICP), premature rupture of membranes (PROM), postpartum hemorrhage (PPH), preterm birth and cesarean section were compared in groups A and B, A1 and A2. The incidence of neonatal asphyxia (SGA), neonatal asphyxia (SGA) and neonatal asphyxia in each group were compared. Results The use rate of insulin during pregnancy and the incidence of maternal complications such as ICP, PPH and preterm birth in group A were significantly higher than those in group B (all P＜0.05), but there was no significant difference in the rate of cesarean section between the two groups (P＞0.05). The incidence of neonatal complications such as neonatal asphyxia and SGA in group A was significantly higher than that in group B (all P＜0.05). The use rate of insulin during pregnancy and the incidence of maternal complications such as HDCP, ICP, PPH and preterm birth in group A1 were significantly higher than those in group A2 (all P＜0.05), but there was no significant difference in the rate of cesarean section between the two groups (P＞0.05). The incidence of neonatal complications such as neonatal asphyxia, SGA and neonatal hypoglycemia in group A1 was significantly higher than that in group A2 (all P＜0.05). Conclusion HBV infection can increase the rate of insulin use in pregnant women with GDM, resulting in increased adverse maternal and fetal outcomes in pregnant women with GDM, and the incidence of insulin utilization rate and adverse maternal and fetal outcomes may be related to liver function.