Ji Kang's health theory is now in Shanghai Museum. According to the relevant information, Ji Kang's Theory of Health Preservation is a real grass in Zhao Gou, Song Gaozong, with a length of 23.5x602.8, which is collected in Shanghai Museum. The Theory of Health Preservation written by Ji Kang of the Three Kingdoms is a famous book of health preservation in early ancient China. This paper discusses the necessity and importance of health preservation, and advocates physical and mental cultivation, especially spiritual cultivation. It is proposed that health care should be based on micro-knowledge, prevent micro-duration, and prevent problems before they happen. It is required that health preservation should be lasting and reasonable, and some specific health preservation ways are put forward.