Ying-nutrients and Wei-defence and qi⁃blood are the basic substances that constitute human body and maintain human life activities. Although Ying-nutrients and Wei-defence and qi⁃blood have been described separately， the relationship between the two is rarely discussed. The syndromes and treatments of Huangqi Guizhi Wuwu Decoction are analyzed through “medicine group method”， the pathogenesis was proved backward by formula treatment （i.e. “Inferring syndromes with formulas”） according to the related theory of formula and syndrome，then the relationship between Ying-nutrients and Wei-defence and qi⁃blood are discussed. It is considered that Ying-nutrients and Wei-defence are derived from the middle jiao， and the upper jiao is pneumatized after the upper spleen is transfused into the heart and lung， and transformed into qi and blood， i.e. “The middle jiao receives qi， takes the juice and transforms into red liquid called blood”. Therefore， Ying-nutrients and Wei-defence are from the middle jiao， change in the upper jiao， with qi and blood homologous but different quality. In this sense， the essence of Ying-nutrients and Wei-defence is qi and blood.