The invention relates to a preparation method of an eleocharis tuberosa flavored additive. The preparation method comprises the following steps: (1) taking fresh eleocharis tuberosa flesh which is abundant in flesh, cleaning the taken eleocharis tuberosa flesh with water of which the temperature is lower than or equal to 30 DEG C, and smashing the cleaned eleocharis tuberosa flesh to obtain eleocharis tuberosa pulp; (2) taking 1 part of the eleocharis tuberosa pulp, adding distilled water of which the weight is 1-2 times of that of the eleocharis tuberosa pulp, then adding an enzyme preparation of which the mass is 0.05-0.1% of that of the eleocharis tuberosa pulp, performing medium-and-low-intensity stirring and leaching under the condition of temperature being lower than or equal to 30 DEG C for 2-3 hours, and taking filtrate; (3) performing vacuum microwave drying under the condition that the temperature is maintained to be lower than or equal to 40 DEG C until powder blocks are obtained; and (4) performing nanometer mechanical pulverization on the powder blocks so as to obtain powdery products of 200-400 nanometers. The eleocharis tuberosa flavored additive prepared by the preparation method disclosed by the invention can be used as an additive for various foods, low-temperature drying is performed by a vacuum microwave drying method, nutrient components and health-care functions of the eleocharis tuberosa flesh are preserved in the products, and the products are powdery, so that the products are convenient to use.