Objective This paper is to provide reference and theoretical basis for safety of modern Tibetan medicine application by literature researching of toxicity understanding in Tibetan medicine. Methodology The study begins with classical literatures of Tibetan medicine and discusses the appearance, development, and evolution of poison in the Tibetan Medicine. It also systemically combines and presents different kinds of theories. Results Tibetan medicine has its unique understanding in toxicity theory. There are four periods including appearance, development, finishing ，and perfection. The definition and classification of the poison and attenuated theory will be discussed in detail. Conclusion There are three main realizations of the poison in the Tibetan medical Classics, such as drugs come with toxicity; toxicity is the bad substance and form of which results in human disease; Toxicity is negative effects of drugs.