Objective To investigate the effect of vitamin D supplementation in early pregnancy on the incidence and glucose metab-olism of high-risk women with gestational diabetes mellitus.Methods Pregnant women who had regular prenatal examination in Hefei First People's Hospital from December 2019 to May 2022 with serum 25(OH)D level＜30ng/ml,expected date of delivery ≥ 35 years or pre-pregnancy body mass index(BMI)≥24kg/m2were selected.They were randomly divided into intervention group(86 cases)and control group(94 cases).The intervention group,took 1200IU/d vitamin D3 capsules orally from the first trimester of pregnancy to the second trimester of pregnancy[the date of oral glucose tolerance test(OGTT)examination for pregnant women];the control group was not given vitamin D3 capsules,and pregnant women with vitamin D deficiency or insufficient were recommended to take vitamin D3 cap-sules or calcium tablets containing vitamin D.Results The levels of vitamin D in the first and second trimester of pregnancy were 12.986± 5.654ng/ml and 31.277±9.856ng/ml in the intervention group,and the difference was statistically significant(P＜0.001).The inci-dence of gestational diabetes mellitus in control group and intervention group was 24.5％and 20.9％,and the difference was not statisti-cally significant(P＞0.05).There were no significant difference in fasting blood glucose,fasting insulin,1h blood glucose,2h blood glucose and homeostasis model assessment insulin resistance index(HOMR-IR)between the intervention group and the control group in the second trimester of pregnancy(P＞0.05).Conclusion Vitamin D supplementation in early pregnancy can only significantly improve the level of vitamin D in pregnant women,and almost make it reach sufficient state,but has no obvious effect on the risk of gestational dia-betes mellitus and glucose metabolism.