This article expounds the formation,connotation and development of the etiology theory in TCM.By analyzing the deficiency of the existent etiology theory in TCM,we proposed that the essence of the etiology theory in TCM should be studied based on the concept of unification of human and nature.With the guidance of the concept of unification of human and nature,the etiology theory in TCM could be formed an integrated theory.The classification of etiology in TCM which includes basic etiology,secondum etiology and developing etiology was proposed,which makes the etiology theory system in TCM more scientific and logical.