Paracelsus, the first person in the history of modern Western medicine, specified to break the shackles of the traditional medical system thoroughly and revolutionise the classical medical system completely. He introduced traditional alchemy into medicine, and changed it from making gold into producing drugs which were helpful to human health. He believed that nature and human were made by God with "three principles" - sulphur, salt and hydrargyrum. He also believed that human body, as a "chemical system", was full of a variety of chemical reactions. His ideas brought a new worldview, a chemical one, to the medical field influenced by the concept of"Humorism" for ages. The chemical worldview laid the foundation for "iatrochemistry" and channelled a path for the following medical development. The "three principles" of Paracelsus did not surpass the "Humorism" proposed by Galen in terms of underlining the balance of human health. However, the idea, that the mineral substances in nature in the "three principles" could be taken as medicines to help the recovery of human body, broke through the traditional medical system proposed by Galen, offered valuable ideological resources and experience for the following expansion and development of medicines.