〔Abstract〕 Objective To investigate the effect of metformin hydrochloride combined with insulin aspartate in patients with gestational diabetes mellitus (GDM). Methods A total of 80 GDM patients admitted to the Obstetrics Department of the First Affiliated Hospital of Zhengzhou University from September 2021 to August 2023 were selected for this study and divided into a control group and an observation group according to random number table method, with 40 cases in each group. The control group was treated with insulin aspartate alone, and the observation group was treated with metformin hydrochloride combined with insulin aspartate. The clinical therapeutic effect, blood glucose index level, insulin index level and adverse pregnancy outcome of the two groups were compared. Results Before treatment, there was no statistical significance in the levels of blood glucose and insulin between the two groups (P > 0.05). After 1 month of treatment, the levels of fasting blood glucose (FPG), 2h postprandial blood glucose (2h PG), glycosylated hemoglobin (HbA1c) and insulin resistance index (Homa-IR) in the observation group were lower than those in the control group, while the levels of fasting insulin (FINS) and homeostasis model assessment of function index (Homa– β) were higher than those in the control group, with statistical significance (P < 0.05). The incidence of adverse pregnancy outcome between the two groups was compared, and the index of the observation group was lower than that 4 the control group, with statistical significance (P < 0.05). Conclusion For GDM patients whose blood sugar level has not achieved a good control effect after diet and exercise control, metformin hydrochloride combined with insulin aspartate therapy can not only control the blood sugar level of the patients at a lower level, improve the function of the islets, but also reduce the occurrence of adverse pregnancy outcomes.