The invention provides a buckwheat shell flavonoid extract. A flavonoid compound in a buckwheat shell is extracted with an ethanol solution as an extracting agent by employing an ultrasonic assisted extraction method, wherein the material/liquid ratio is 1 to 30; the extraction time is 15 minutes; the ethanol concentration is 80%; on the basis of the extraction condition, the yield of buckwheat shell flavonoid and the scavenging rate of DPPH (diphenyl picryl hydrazinyl) free radical are respectively 1.60% and 85.62%; the extracted buckwheat shell flavonoid is separated and refined with porous resin; the technological parameters are as follows: the adsorption flow rate is 2mL/min; the mass concentration of sampling liquid is 6.0mg/mL; the column loading volume is 2-3BV; the washing volume is 3BV; the ethanol concentration of an eluent is 70%; the eluting flow rate is 2mL/min; the resin can be repeatedly used for six times; the purity of the buckwheat shell flavonoid can be improved to 76.17% from 30.82%; the purity is improved by 2.47 times; through a model test for rats with type 2 diabetes mellitus, the buckwheat shell flavonoid extract has a relatively good improvement effect on rats with the type 2 diabetes mellitus; and the hpoglycemic effect is superior to that of metformin hydrochloride. An experiment proves that the buckwheat shell flavonoid extract is a mixture and also contains other unknown substances besides flavonoids and flavonoid compounds.