This invention discloses the preparation and the application of Grain Worm for treating diabetes or regulating blood insulin level. The Grain Worm can be in the form of dry powder, tincture, or extracts by itself or in a compound. Grain Worm regulates the blood insulin levels and the human blood glucose level for treating diabetes. It has been discovered that Grain Worm can effectively treat diabetes in humans through reducing insulin resistance and improving the β-cell function. The effect of this agent can last a long period of time (2-5 years). This is the first major discovery of using Grain Worm in treating diabetes.