The invention discloses a preparation method of tartary buckwheat red yeast rice. The method comprises the following steps: immersing tartary buckwheat in water, washing, draining, steaming, cooling in aseptic environment, and cooling to obtain cooked tartary buckwheat; adding 15-25g of monascus powder, 0.2-0.5g of acetic acid and 0.01-0.03g of yeast to 5-15g of sterile water, and stirring and breaking for uniform mixing in order to obtain an inoculation strain; uniformly mixing and stirring the inoculation strain and the cooked tartary buckwheat according to a ratio of 1-15:100, and carrying out fermentation culture at 30-40DEG C; and drying after the fermentation culture ends in order to obtain the tartary buckwheat red yeast rice. The monascus and yeast are co-fermented, tartary buckwheat is adopted as a substrate, and the oxidation resistance of the tartary buckwheat red yeast rice product is improved through adjusting culture conditions.