Tongue diagnosis is an important part of Traditional Chinese Medicine,and it is the main method for understanding the physiological functions and pathological changes of human body,its basic principle is the " image thinking" of conjecturing the interior by observing the exterior,which is to explore the physiological and pathological status of human body by observing the changes of tongue quality and tongue coating, as an important method for examining diseases and syndrome differentiation. In this paper,the connotation of tongue diagnosis will...