In recent years, much evidence has shown that vitamin D not only plays important roles in bone diseases, but also plays more vital roles in non-bone diseases. Basic studies confirmed that vitamin D receptors are extensively expressed in various cells in the body. In clinical studies, vitamin D supplementation is essential in the prevention and treatment of tumors, metabolic syndrome, cardiovascular diseases, and autoimmune diseases. In this paper, we reviewed the progress in researches on vitamin D deficiency and above-mentioned diseases.