Abstract： Objective To explore the influencing factors of type 2 diabetes mellitus(T2DM)complicated with metabolic syndrome(MS)and investigate the correlation between the level of 25(OH)D3 and T2DM combined with MS.Methods 592 in patients with T2DM admitted to the Department of Endocrinology of Shenzhen Second People's Hospital were selected from January to December 2020.They were divided into simple T2DM group(T2DM,n=194)and T2DM combined with MS group(MS,n=398).Results Compared with the T2DM group,the MS group had lower 25(OH)D3 levels[26.30(20.50,32.39)vs 24.20(20.16,29.47),P<0.05].Spearman correlation analysis showed that 25(OH)D3 was negatively correlated with MS,FPG,TG,LDL-C,and 24 hUAlb(P<0.05 or P<0.01).Logistic regression analysis showed that 25(OH)D3 was a protective factor for T2DM combined with MS.Conclusions Patients with T2DM and MS have lower 25(OH)D3 levels.25(OH)D3 is a protective factor for T2DM combined with MS.