Abstract: Insulin resistance and islet cell dysfunction are the main pathogenesis of type 2 diabetes. The generation of a great quantity of mitochondrial reactive oxygen species (ROS) impairs the function of mitochondria and induces oxidative stress during metabolic process of hyperglycaemia and hyperlipemia. Oxidative stress results in: (1) block the insulin action pathway and induce insulin resistance; (2) depress the expression of insulin gene; (3) decrease insulin secretion; (4) impair cell function. In this paper, we summary the mechanism of the ROS generation, insulin resistance and cell dysfunction induced by oxidative stress.