The invention discloses a preparing method of nutritious rice flour, belongs to the technical field of food processing and particularly relates to a preparing method of nutritious rice flour. The method includes adding water and cane sugar into food-grade rice protein powder, fully stirring, sterilizing, inoculating with aspergillus oryzae, fermenting, boiling after fermentation is finished, cooling to obtain a sterilized fermentation liquid, fully mixing germinated brown rice flour and the sterilized fermentation liquid, hydrolyzing, filtering to obtain filtrate, subjecting the filtrate to concentration and spray drying to obtain refined dry flour, and fully mixing puffed rice flour and the refined dry flour according to a mass ratio of 10:1 to obtain a finished product. The nutritious rice flour prepared by the method contains large amounts of amino acids and rice peptides, is rich in functional components such as gamma-aminobutyric acid, and has good healthcare functions for human bodies.