Qingfei Paidu Decoction has been proved in clinical practice to be an effective prescription for treating COVID-19.It is derived from four ancient classical prescriptions and has great values for theoretical mining and inheritance.Among the four classical prescriptions,Maxing Shigan Decoction disperses and purifies lung qi; Wuling Powder warms yang qi; Shegan Mahuang Decoction warms lung and resolves fluid retention; Xiaochaihu Decoction harmonizes lesser yang.According to the rule of prescription formation,Ephedrae Herba and Asari Radix et Rhizoma disperse and purify lung qi by ascending and descending qi,being the sovereign herbs; Poria,Polyporus,Alismatis Rhizoma,Dioscoreae Rhizoma,Pogostemonis Herba,Armeniacae Semen Amarum,Cinnamomi Ramulus,and Atractylodis Macrocephalae Rhizoma warm yang qi,promote urination,and dry dampness,being the minister herbs; Zingiberis Rhizoma Recens,Pinelliae Rhizoma,Citri Reticulatae Pericarpium,Aurantii Fructus Immaturus,Belamcandae Rhizoma,Asteris Radix et Rhizoma,Farfarae Flos,and Bupleuri Radix harmonize stomach,descend adverse qi,benefit qi,and dispel phlegm,being the assistant herbs; Gypsum Fibrosum and Scutellariae Radix clear lung,resolve phlegm,descend adverse qi,and relieve cough,being corrigent; Glycyrrhizae Radix et Rhizoma harmonizes all the medicinal members in the prescription,being the guide herb.The compatibility of Qingfei Paidu Decoction aims to regulate the ascending and descending of qi and remove the pathological products of cold-dampness and stasis toxin.