Meridian theory is one of the core fundamental theories of Traditional Chinese Medicine (TCM).It makes acupuncture in clinical treatments possible,So most researches in meridian nature,over five decades\' history of the People\'s Republic China,have been focusing on experimental studies with scientific and technical measures such as acoustics,optics and so on. However,they failed to break through and to achieve generally accepted results,Therefore the nature of meridian remains a challenging issue.This paper tries to prove the nature of meridian from another angle using mathematics method.The purpose is to seek a new path and to break through the deadlock in experimental studies.Such a result can show scientific connotation of TCM basic theory and contribute to its future development.This paper proves the nature of meridian using the set theory.It shows that the meridian in nature is a comprehensive function system composed of nervous system,blood vessel circulatory system,lymph system(except spleen) and endocrine system.These sub-systems,which form the material base of meridian,are responsible to meridian nature\'s physiological functions and pathological changes.The innovation of this study is to prove the nature of meridian from mathematics angle using set theory.