Constitution is an important factor to determine the susceptibility and the occurrence of disease. This article analyzed causes and characteristics of damp-heat constitution, the change of damp-heat constitution to damp-heat syndrome, the relationship between damp-heat constitution and the occurrence and development of diabetes mellitus. It reached the conclusion that damp-heat constitution is one of the important factors of diabetes mellitus, that damp-heat syndrome is always accompanied with the development of diabetes, and proposed the treatment methods of lifestyle intervention, elimination of pathogens through purgation and diuresis, nourishing yin and dredging the collaterals. It also proposed the new ideas and thoughts of early intervention in damp-heat constitution and distinguishing constitution therapy for the prevention and treatment of diabetes mellitus.