A preparation method of a functional beverage containing Lespedeza cuneata and Rubus coreanus Miquel is provided to remove the bitter and pungent taste of Lespedeza cuneata root without using any artificial sweetener. A preparation method of a functional beverage containing Lespedeza cuneata and Rubus coreanus Miquel comprises the steps of: (i) washing Lespedeza cuneata and Rubus coreanus Miquel, and cutting them fine; (ii) grinding the cut Lespedeza cuneata and Rubus coreanus Miquel, settling them with ethanol, and aging; (iii) filtering the aged mixture of Lespedeza cuneata and Rubus coreanus Miquel to collect an extract; (iv) sterilizing the collected extract while distilling off the ethanol contained in it at 78.3°C or above; (v) mixing 0.1~1g of an antioxidant and 10~20g of at least one side ingredient selected from the group consisting of a plant extract, a medicinal herb extract, and a mushroom extract to 100g of the collected extract of Lespedeza cuneata and Rubus coreanus Miquel; and (vi) diluting t
