The acute respiratory distress syndrome(ARDS)is an acute hypoxic respiratory insufficiency caused by severe infection,shock,trauma and burns.It is easily confused with severe pneumonia combined with hypoxemia and severe COVID-19 pneumonia.In this paper,the concept,pathogenesis,pathological changes,pathophysiology and definition of ARDS were discussed,and the similarities and differences between ARDS and severe pneumonia combined with hypoxemia or severe COVID-19 pneumonia were analyzed and conducted in-depth interpretation.