The invention discloses nutrient solution for cultivating selenium-rich rice. A method for preparing the nutrient solution includes 1), preparing raw materials including 100 parts of purified water, 1.5-2.5 parts of L-selenomethionine and 0.5-1.0 part of hydroxyethyl celluloses; 2), mixing the raw materials prepared at the step 1) with one another to obtain mixtures, placing the mixtures in a steam explosion tank under the pressure of 4 MPa, heating the mixtures until the temperatures of the mixtures reach 150 DEG C, keeping the temperatures of the mixtures unchanged for 2 min, then quickly releasing the pressure within 1-3 s to obtain serous fluid, inoculating cultured mature bacillus subtilis liquid strains into the serous fluid at the temperature of 25 DEG C according to a volume percent of 5-10%, placing the serous fluid and the bacillus subtilis liquid strains in a fermentation tank, filling the fermentation tank with sterile air, stirring and fermenting the serous fluid and the bacillus subtilis liquid strains to obtain products, quickly increasing the temperatures of the products until the temperatures reach 70 DEG C after the serous fluid and the bacillus subtilis liquid strains are completely fermented, keeping the temperatures unchanged for 0.5-1.0 h and inactivating the products to obtain the nutrient solution.