Three years. A three-year apprenticeship in traditional Chinese medicine is equivalent to three years of secondary education. Traditional Chinese medicine is a comprehensive science which focuses on the theory and practical experience of traditional Chinese medicine and studies the transformation law of health and disease in human life activities and its prevention, diagnosis, treatment, rehabilitation and health care. The theory of TCM comes from the summary of medical experience and China's ancient thought of Yin-Yang and Five Elements. Its contents include the theory of essence and qi, the theory of yin and yang and five elements, qi and blood, body fluid, viscera and meridians, constitution, etiology and pathogenesis, treatment principles, health preservation and so on. As early as more than two thousand years ago, the monograph Huangdi Neijing came out, which laid the foundation of traditional Chinese medicine.