To explore the glucose and lipid metabolism situation and the level of serum 25(OH)D of pregnant women with gestational diabetes mellitus (GDM) during the first trimester of pregnancy, and to observe the intervention effect of vitD combined with diet control for treating overweight pregnant women with GDM.Methods: A total of 167 overweight pregnant women were prospectively selected as study subjects from September 2019 to March 2020.Based on the occurrence of GDM, these women were divided into group A (61 women without GDM) and group B (106 cases women with GDM).30 healthy pregnant women with BMI <24kg/m2 were selected in group C during the same period.The situation of glucose and lipid metabolism and the 25(OH)D  level of the women in the three groups were measured during 12 gestational weeks.In group B, 63 women only given diet control during 24 gestational weeks were included in group B1, and 43 women given diet control combined with vitD during 24 gestational weeks were included in group B2.The HOMA-IR value and the adverse clinical outcomes of the women in group B were assessed dynamically.Results: There were significant differences in the levels of serum fasting blood glucose (FPG), glycosylated hemoglobin (HbA1c), total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), and 25(OH)D, and the HOMA-IR value of the women during the first trimester of pregnancy among group A, group B, and group C.Pearson analysis showed that 25(OH)D level of the women was negatively correlated with their FPG, HbA1c, and TC levels, and their HOMA-IR value, and the 25(OH)D level was positively correlated with their HDL-C level (all P＜0.05).The HOMA-IR value of the women in group B had decreased with the increasing of gestational weeks, but which of the women in group B2 in 1, 2, or 4 weeks after intervention was significantly lower than that of the women in group B1 (all P＜0.05).The total incidences of adverse pregnancy (11.6%) and adverse neonatal outcomes (9.3%) in group B2 were significantly lower than those (23.8% and 27.0%) in group B1 (P＜0.05).Conclusion: There are differences in the levels of glucolipid metabolism and 25(OH)D between overweight pregnant women and normal pregnant women.Dietary control combined with VitD intervention of overweight pregnant women with GDM can effectively reduce their HOMA-IR value and reduce the adverse clinical outcomes of mothers and infants.