The invention discloses a material grain separation technology used after shelling shells during processing of buckwheat. The technology comprises the steps that 1, after the shells of the buckwheat are separated, a mixed material containing a small part of buckwheat husks, buckwheat grains and the buckwheat with the shells is screened through a vibration grading screen at first, oversize products on lower layer screen cloth enter a color sorter through an elevator and the colors of the oversize products are sorted and separated, color sorting is conducted three times sequentially, separated semi-finished buckwheat grains are screened and graded through the vibration grading screen, and high-quality finished buckwheat grains are obtained; 2, small-grain-type buckwheat with the colors being sorted for the first time and the second time is uniformly mixed with large-grain-type buckwheat intercepted by upper layer screen cloth, wherein the small-grain-type buckwheat and the large-grain-type buckwheat are provided with the shells, and after cooling-heating treatment is conducted, the buckwheat enters a huller in batches for secondary shelling; and 3, the final material grain separation rate reaches 99.9%, the secondary shelling rate reaches 95%, the purity of the buckwheat grains can reach 99.9%, the imperfect grain mass is 1% or less, impurities account for 0.10% or less, broken grains account for 1% or less, the surface of the buckwheat is bright and clean, and the buckwheat has obvious buckwheat fragrance. The purpose of large-scale material grain separation with high quality, high efficiency and high yield is achieved for the buckwheat grains with the shells being separated.