The invention relates to the field of selenium-rich rice byproducts, and in particular relates to a preparation method of rice bran selenoprotein powder. The method comprises the following steps of: grinding, screening and degreasing byproduct rice bran obtained after rice processing to prepare rough rice bran into degreased rice bran, mixing 60%-70% alcohol with the degreased rice bran in the material-liquid ratio of (1:3)-(1:5), stirring on a magnetic force mixing machine for a certain period of time, and centrifuging, wherein the processes are repeated for three times; and carrying out alkaline extraction with 0.02-0.1mol/L NaOH solution for 1-3 hours in the material-liquid ratio of (1:10)-(1:20) at the temperature of 30-40 DEG C, taking supernate after centrifuging, decolorizing with active carbon, adjusting an isoelectric point by utilizing a acetic acid-natrium aceticum buffer solution for acid deposition, then centrifuging, and freezing to dry after washing, thereby obtaining the rice bran selenoprotein powder with the protein extraction ratio of 60-80%, and the selenium content of 0.2-0.3mg/kg finally. The selenoprotein powder provided by the invention is natural in nutritional ingredient, is rich in trace element selenium, keeps the original nutrition ingredients in the rice bran selenoprotein powder effectively, and is suitably used as a food auxiliary material or a nutrition enhancer.