The invention provides a granule composition for preventing and treating diabetes by a broad bean dietary therapy method and a preparation method thereof, and relates to the technical field of functional health-care products. The granule composition for preventing and treating the diabetes by the broad bean dietary therapy method is mainly prepared from the following components of broad bean, semen nelumbinis, poria cocos, endothelium corneum gigeriae galli, rhizoma dioscoreae, semen euryales, semen coicis and radix puerariae, wherein the broad bean is used as the monarch drug, has the functions of tonifying the spleen and removing dampness, and can well improve the spleen deficiency and health lack condition of the diabetes patient; the semen nelumbinis, the semen euryales and the semen coicis are used as the ministerial drugs, and have the effects of tonifying the spleen and invigorating the spleen, as well as nourishing the heart and calming the mind; the poria cocos, the endothelium corneum gigeriae galli and the rhizoma dioscoreae are used as the adjuvant drugs, and have good dampness removal effect; the radix puerariae is used as the conductant drug, and has the good meridiandredging and collaterial activating effects. The compounded granule composition for preventing and treating the diabetes by the broad bean dietary therapy method has the advantages that the functionsof tonifying the spleen and invigorating the kidney as well as nourishing and strengthening are realized; the immunity of a human body is enhanced; the content of blood glucose in blood and cells isregulated; the human body is promoted to absorb and utilize the glucose; the granule composition is used for assisting to treat the diabetes.