Abstract: Provided is a use of mesenchymal stem cells in the preparation of a drug for repairing lung damage caused by COVID-19. It is proved by clinical tests for the first time that mesenchymal stem cells have an excellent effect on repair of lung damage in subjects with viral pneumonia, especially severe pneumonia caused by SARS-CoV-2 infection, and can significantly reduce solid component lesion volume of the subjects, and repair lung tissue; moreover, it is proved by means of a six minute walking test that mesenchymal stem cells can significantly repair the subjects' cardiopulmonary function, so that the aerobic exercise capacity is significantly improved, thereby effectively alleviating sequelae of the subjects after the end of antiviral treatment, and improving health and quality of life of the subjects; in addition, mesenchymal stem cells are highly safe, and no obvious adverse reactions have been found.