In an apparatus for producing U3O8 powder, the apparatus has an oxidation reactor including an interior space, a scrap box loaded with UO2 sintered pellets to be oxidized and introduced into the interior space of the oxidation reactor, an impact generating unit applying an impact to the scrap box to dissipate heat generated by the oxidation of the UO2 sintered pellets in the oxidation reactor, and a control unit controlling an oxidation process. The apparatus for producing U3O8 powder allows the heat generated by the oxidation of the UO2 sintered pellets in the oxidation reactor to be uniformly dissipated by the impact generating unit, thus producing U3O8 powder having a larger specific surface area which can be used to obtain a sintered UO2 pellet with a larger and more stable grain size of increased quality.