Dan, Shan Ye, Yi, Shan Ye. Only the Tao is not right, so it is called Dan. The sky is high and the clouds are light, the ground is flat, the valley is full, and people are immortal. Inner alchemy is a practice mode which is guided by the idea of harmony between man and nature, takes the human body as a cauldron, takes essence as medicine and condenses in the body. Since Huangdi, the ancestor of Taoism in China, recorded his quest for Taoism in Guang Cheng Zi, Neidan has experienced a development process of 5,000 years. The ancestors of Dan Daozu spread the origin of Dan Daoism very early. Tao Te Ching, Wen Zi, Liezi, Zhuangzi, Internal Strength, Xin Xue, Chu Ci, Yuan You, Yin Fu Jing and the works of Huang Lao School are the ancestral scriptures on which all the Dan Classics must be based, and all the Dan Classics in later generations developed from them, which has always been the outline of the internal Dan method.