Diabetic nephropathy is one of the most common complications of type 2 diabetes mellitus (T2DM), which is one kind of the damage of renal function caused by microvascular damage, whose occurrence and development mechanism are complex. The deficiency and deficiency of vitamin D may be correlated with the occurrence of diabetic nephropathy. Vitamin D is widely used as calcium phosphate regulator in clinic. In recent years, studies have shown that patients with T2DM with nephropathy exist severe vitamin D deficiency. Having the activity of vitamin D plays a protective role in the development of T2DM and diabetic nephropathy progress. This effect is not the same as the classical calcium phosphate adjustment mode. This paper will make a brief discussion about the study correlation between the 25-hydroxy vitamin D levels and diabetic nephropathy.