To study the hypoglycemic effect and mechanism of the extracts of cactus pear fruit polysaccharide (CPFP) in diabetic rats induced by streptozotocin (STZ).The diabetic rats were induced by STZ in SD rats, and randomly divided into model group, insulin group,cactus pear juice group, high dose CPFP group,low dose CPFP group. The experimental rats were administrated for 8 weeks. During the experiment, the contents of blood glucose and blood limit of the rats were detected and body weight were recorded. The pathology of beta cell and alpha cell in pancreas of experimental rats were observed by immunohistochemistry.Compared with model group, the contents of blood glucose, total cholesterol and triglyceride were remarkably decreased in high and low dose CPFP groups. At the same time the body weight was significantly increased in high dose and low dose CPFP groups. The results of immunohistochemical stain demonstrated that the number of islet beta cells was increased and that of islet alpha cells was unchanged in the treatment groups.CPFP can markedly decrease blood glucose and blood limit in STZ-induced diabetic rats. Its mechanism may be related to stimulating the secretion of insulin from beta cells.