The saints of Huayan School regarded the mind as the basic concept to interpret Buddhism theory. The statements on the metaphorical speech of the painter and Mind-only in three realms in Avatamsaka Sutra provide a reliable literature basis to bring up and explain the concept of "one-mind". The Awakening of Mahayana Faith and Ten Stages Sastra provide pre-understanding about it for founders of Huayan School in Tang Dynasty, succeeding the theory of one-mind of Avatamsaka Sutra. Huayan School develops understanding of one-mind in four dimensions including four dharma taken in one-mind from the perspective of spiritual essence of Dharmadhatu, ten mysterious gates taken in one-mind from the perspective of mind operation, five teaching taken in onemind from the perspective of teaching classification and creative understanding on mind-only in three realms in Avatamsaka Sutra. The scholars of Huayan School focus on applying one-mind to its teaching and highlight the theoretical characteristic of distinct teaching of the single vehicle which Huayan theory is based on one-mind.