Endothelial cell dysfunction is an important initial event of diabetic vascular complications. Hyperglycemia induces various metabolic alterations, such as the elevation of oxidative stress, activation of abnormal metabolic pathways, accumulation of advanced glycation end products (AGEs) and activation of protein kinase C (PKC) pathways, and all of these alterations can lead to endothelial cell injury. Therefore, how to inhibit abnormal metabolism and improve the functions of endothelial cells is the key point of diabetic vascular complications. In this article, we reviewed the abnormal metabolism of endothelial cells in diabetic patients.