Our study confirms that vitamin D deficiency and insufficiency are more prevalent in T1D, and that CYP2R1 (rs1993116) polymorphism is a candidate gene for susceptibility to T1D in Chinese children, There was a synergistic effect of gene-gene interactions between CYP2R1 (rs12794714) and CYP2R1 (rs1993116) on the risk for T1D, Vitamin D metabolic pathway gene polymorphism, and gene-gene synergy can better explain the effect of vitamin D on the pathogenesis of T1D. The gene discussed is CYP2R1; the disease is type 1 diabetes mellitus.