There were complicated biochemical changes in rice grains, and dry matter of rice was accumulated and moisture content of rice decreased gradually during rice maturity. Post-harvested rice grains were fractionated by kernel thickness with grader of slotted screen; there were differences of physical, physicochemical and milling characteristics among grains in various thickness sections. This fractionating process by kernel thickness improved uniformity among grains and applicability of processing product of rice，and the relative characteristics on fractionating process to rice grains could be applied in drying, storing and milling with better the applicability.