Combined with the Diagnosis and Treatment Plan of Pneumonia Infected by Novel Coronavirus (7th trial version) promulgated by the state, the etiology and pathogenesis of COVID-19 were analyzed from the four stages of dampness, heat, toxin and deficiency. It is considered that COVID-19 can be divided into mild-syndrome (such as cold and dampness stagnation in the lung and accumulation of dampness and heat in the lung), common-syndrome (such as stagnation of dampness and toxin in the lung and cold and dampness blocking the lung), severe-syndrome (like blockage of pulmonary qi by pestilent toxin and intense heat in both qifen and yingfen), critical-syndrome (internal obstruction and external collapse), and lung and spleen qi deficiency and dual deficiency of qi and yin in convalescent stage. The diagnosis and treatment strategies and prevention ideas were discussed in each stage.