Constitution is the basis of the occurrence and development of diabetes and its complications.Different constitutions are formed due to the imbalance of physiological functions.Because of the different constitution,the occurrence and development of any kind of disease is inevitably influenced by transformation according with constitution.Therefore,in clinic,only from three aspects——constitution differentiation,disease differentiation and syndrome differentiation,one can comprehensively grasp the root cause of a disease when making syndrome differentiation and treatment of diabetes and its complications.