Glycemic Index, proposed by Dr.Jekins in 1970, was an index that measured blood sugar capacity of food. Recent research indicated that glycemic index had positive effects on therapy of diabetic patients and weight management for the overweight. In this paper, the author introduced the concept of glycemic index, food materials grading based on GI, the relationships between GI and food components, the physiological reaction of human separately consuming high GI or low GI food, the application of GI in prevention and cure of diabetes. The review will provided scientific evidences for medical treatment and designing nutritional meal for diabetic patients in comtemporary medical science.