Abstract： Wenyi Lun holds that “abnormal climate” is the etiology of communicable disease(epidemic) at Ming dynasty. Coronavirus disease 2019(COVID- 19)， with strong infectiousness， belongs to the category of “epidemic” in Chinese medicine. In this paper， the pathogenic mechanism of COVID- 19 as well as its prevention and treatment are discussed from the pathogenic characteristics of dampness toxin. Dampness toxin is characterized by heavy turbidity，sticky and lingering， which is manifested in clinical syndrome and a long course of disease， etc. Most obese people have the constitution of yang deficiency and dampness excess；if infected，they are easy to have a variety of syndromes due to the inward invasion of epidemic pathogen and develop into a severe case. The prevention and treatment should focus on resolving dampness and eliminating toxin； meanwhile， it should protect the spleen and stomach as well as the fluid and humor. Besides，we should pay more attention to prevention than treatment and give full play to the characteristics and methods of Chinese medicine in preventing disease before it arises， so as to enhance immunity and avoid the invasion of pathogenic toxin. In addition，we should adjust measures according to the place，person，time and syndrome，and have a good grasp of the relationship between reinforcing the healthy qi and eliminating pathogenic factors； more attention should be paid to "keeping healthy qi inside to prevent the pathogenic toxin". In this paper，it is pointed out that the key to the prevention and treatment of COVID-19 is the understanding of and solutions to dampness toxin and pathogenic qi. It is hoped that Chinese medicine can fully play its role and advantages in the prevention and treatment of the epidemic.