Abstract: This paper presents an exploration into the theory of flaccidity syndrome in Canon of Medicine.The author points out that etiology of the disease include external invasion and internal damage,pathogenesis include heat of the five zang-organs,lung heat,and deficiency of Yangming,causing flaccidity as a result of failure in nourishment,and treatment of the disease include such methods as treating Yangming alone,reinforcing the Ying-points to remove obstruction and giving treatment according to seasonal conditions.These theories are still of great guiding significance for modern clinical practice.