Tantric Buddhism Sutra was firstly translated into Chinese and spread in China in the late Han and early Wei Dynasties. In the Tang Dynasty, Tantric Buddhism school was founded and its practice was widely accepted by both government officials and common people. Although it was greatly weakened due to the catastrophe that Buddhism suffered during the period of Huichang in the Tang Dynasty, Tantric Buddhism, with its secularization, had penetrated into the daily life of common people. For instance, the custom of five-color strings and the folk practice of Tantric Buddhism impacted upon one another. Influenced by the doctrines of Five Agents, there had been the custom of wearing five-color strings to avoid and drive out evil spirits in the Dragon Boat Festival since the Han Dynasty. However, in the Song Dynasty, it was combined with the Great Compassion Mantra of Tantric Buddhism and then Candraprabha, one of its main Buddhas. With such enchantment, people began to wear five-color strings not only in the Dragon Boat Festival but in the Double Seventh Festival as well, and this custom was even transformed into the “Daughter’s Festival” in some places. A historical study of this custom helps us not only represent the special folk culture in the Tang and Song Dynasties but also understand better the social life and religions at that time.