Abstract: The disclosure discloses a composition containing melatonin as an effective ingredient, and its application in improving DHI production performance and improving milk quality. The composition containing melatonin as an effective ingredient according to the present disclosure can significantly reduce the somatic cell count in milk and improve milk quality. Under the conditions of different seasons, ages, and lactation periods, the administration of the composition containing melatonin as an active ingredient according to the present disclosure can significantly reduce the somatic cell score of cow milk (p<0.01), increase the protein content and lactose content in milk, and meanwhile reduce the fat content and urea nitrogen content in milk. In summary, the composition containing melatonin as an effective ingredient according to the present disclosure can improve the quality of milk and increase the efficiency of dairy cow breeding.