ACE2 and COVID-19: In order to reduce the mortality of COVID-19 and gain insight into the study of SARS-CoV-2 causing the ARDS and to develop a broad spectrum of drugs as early as possible, this paper analyzes the possible mechanisms of SARS-CoV-2 causing ARDS in angiotensin-converting enzyme 2, cytokine storm, immune cells, Fas/FasL pathway, JAK/STAT pathway, NF-κB pathway, type I interferon, and vitamin D. Their importance in COVID-19 and the possible mechanisms of lung damage are described.