Nutrient-Qi and-defensive-Qi theory is an important part to compose vessel-collateral theory. Suncollateral（ 孙络）

as the smallest unit of vessel-collateral

is the place where nutrient-Qi and defensive-Qi rendezvous and transform. By comprehensively analyzing basic concepts of vessel-collateral theory and nutrient-Qi and defensiveQi

as well as the effect of sun-collateral in the process of-Qi and defensive-Qi rendezvous and transformation and in the process of disease onset

the authors hold that the proposition of nutrient-Qi and defensive-Qi "rendezvous and transformation by collateral"theory of vessel-collateral theory has both solid foundation of Chinese medicine theory and strong evidence of modern medicine. Meanwhile

the results achieved in clinical treatment and in vivo and in vitro experimental study may prove the scientificalness and clinical practicability of this theory.