”Yin Yang Lun” is the core theory of Chinese Medicine. It has instructed the clinical diagnosis of Chinese Medicine and the utilization of medicine for thousands of years. Except the contents such as (1) Setup of contrast, (2) mutual basis and usage, (3) balance of growth and decline, and (4) mutual transformation specified in ”Basic Theory of Chinese Medicine”, it also includes (5) infinite division, (6) both true and false, and (7) the leading factor of Yang. Zheng Chin-An, well-known doctor of Sichuan in latter stage of Ching Dynasty, had applied ”Yin Yang” very well. So this text describes the Yin Yang theory by using his thought. The viewpoints of the successors of ”Fire-God Faction”, Liu Lie-Hon, Lu Chong-Han, Jue Wai-Cheh etc., are referred at the same time.