The invention belongs to the technical field of daily health care, and particularly relates to herbal mouthwash and a preparation method thereof, the herbal mouthwash comprises the following components: by mass, 3-9 parts of green tea, 5-10 parts of stevia rebaudianum, 2-6 parts of borneol, 5-13 parts of honeysuckle, 10-15 parts of mulberry leaf, 4-9 parts of hemianthus micranthemoides, 10-25 parts of gallnut and 500-1000 parts of water. The herbal mouthwash can eliminate bad breath, clear the mouth filth, sterilize, remove dental plaque, prevent or inhibit various oral diseases, prevent tooth decay, improve periodontal diseases, and clean the oral cavity.