To discuss the etiology, pathogenesis, diagnosis and treatment of COVID-19 based on the theory of febrile diseases. The theory of febrile diseases, derived from the accumulation of TCM classical theories and developed through the practice of plague prevention and treatment, has a systematic discussion on the etiology, pathogenesis, pattern identification and treatment of exogenous febrile diseases including virulent ones. It also has played an active role in the prevention and treatment of novel infectious diseases in China in recent years. “Warm-febrile diseases” and “plague” are interlinked. Plagues are mainly caused by heat toxin and epidemic pathogens, manifested as heat pattern and yang pattern, and can be treated according to the disease stages differentiated by “Wei-Qi-Ying-Xue or “Sanjiao” pattern identification methods, or treated with the prescriptions from famous ancient doctors such as Wu Youke and Pang Anshi, etc. These theories related to causes, mechanism, patterns and treatment may be helpful for the TCM diagnosis and treatment of COVID-19. In addition, the lungs and large intestine form an exterior and interior relationship, and the gastrointestinal tract is also the place where SARS-CoV-2 invades or proliferates, it may be a way to reduce virus infection and lung inflammation in the body by adopting the TCM method of clearing heat and dredging the lower part to give pathogenic factors a way out from the bowels.