Critically ill patients with coronavirus disease 2019 (COVID-19) have a high case fatality rate. Hence, controlling the disease progression of severely ill COVID-19 patients to avoid the development of severe-to-critical COVID-19 is the most important target of COVID-19 treatment. The latest autopsy results of COVID-19 patients have shown the presence of viscous secretions in the airways. However, no studies are available that specifically describe and analyze the sputum characteristics and the effects of various sputum drainage methods on the prognosis of COVID-19 patients. In our study, we found that elderly COVID-19 patients were more susceptible to progression to critical illness (P = .024) and were likely to have accompanying lymphopenia (P = .035) or increased neutrophil counts (P = .019). We observed that there was a higher proportion of patients with Grade 3 sticky sputum in the critically ill group than in the noncritically ill group (P = .026), suggesting that changes in sputum characteristics may be one of the early warning signs of critical COVID-19. In addition, we found that the application rates of large doses of ambroxol (P = .043) and prone-position drainage (P = .037) were relatively high in COVID-19 patients with good prognoses, suggesting that the early application of large doses of expectorant drugs and prone-position drainage in COVID-19 patients may avoid progression to critical illness and improve the prognosis.