PURPOSE: A production method of functional coffee beans is provided to reduce the amount of caffeine in the coffee beans using medical herbs, and to maintain the unique taste and flavor of coffee. CONSTITUTION: Medical herbs are mixed and crushed to obtain medical herb powder (s101). The medical herb powder is sterilized using steam. The medical herb powder is dipped in Cordceps militaris strain liquid, and steamed to obtain steamed medical herbs (s102). The steamed medical herbs are sterilized, and mixed with Aspergillus oryzae strains and fructooligosaccharide, and fermented to obtain fermented medical herbs (s103). The fermented medical herbs are mixed with ethyl alcohol, and extracted to obtain a fermented medical herb extract (s104). The fermented medical herb extract is filtered by using kaolin, filter paper, a filtering device, or a glass-filter-4G before being decompress-concentrated (s105). The decompress-concentrated fermented medical herb extract and germinated coffee beans are mixed and steamed (s
