It is very difficult to realize the universal law of the occurence of diseases in terms of Chinese Medicine. The research focused on "Huang Di Nei Jing"(Nei Jing, 內 經), with the use of document analysis (文獻分析法) which includes the interpretation and the comparative research of the texts in Nei Jing or other related annotated edition, philosophical dictionaries and books, aimed to explore the academic thought and theory related to the causes and mechanism of the happening of diseases. The results show that diseases are the consequences of the abnormal effects of Ren Dao (Dao of Human life, 人的生命之道) and the effects can be elaborated concretely through the gradual process of change as followed: various causes → destroy Qi (氣) of different part of the human body → irregular effect of Yin and Yang (陰陽) → irregular interaction between Yin and Yang. The process is based on the universal law of the occurrence of universe and is part of the main content of Bing Ji (病機). Bing Yin (causes, 病因) and Bing Ji refer to the causes and the gradual process of change from Ren Dao to indivisual disease. The result of the research will help to realize the concrete mechanism of the occurrence of individual disease or Zheng Hou (the abnormal appearance of human body, 證候), reduce the chance of misjudgement of Bing Ji, and understand the direction and model of Zheng Hou Thinking (辨證).