Disclosed is a method of preparing a knitting yarn having a water-repellent function, including providing a knitting yarn in the form of a skein or a cone, washing the provided yarn to remove impurities and oil therefrom, coating the washed yarn with a water-repellent agent by spraying a water repellent solution containing the water-repellent agent at a predetermined pressure, dehydrating and drying the coated yarn, and fixing the water-repellent agent to the yarn by applying heat to the dried yarn.