Through review and analysis on description of bloodletting therapy in ancient medical classics, it is found that bloodletting therapy can be classified as two categories of reinforcing and reducing. And the classification is related with many factors such as the quantity of blood, apparatus selected, depth of acupuncture, points selected and physical conditions, etc. Bloodletting therapy is not confined only in excessive syndromes, it is also applied to the treatment of complicated syndrome of excess and deficiency as well as deficiency syndrome with excessive manifestations and deficiency syndrome.