COVID-19 is a new disease which is caused by betacoronavirus. The diameter of the virus particle is very small, about 60~140 nm; therefore, it is easy to reach the lung terminal structure, such as alveolar septum, alveolar wall, and interlobular septum, which causes extensive edema and lymphocyte infiltration in the lung interstitium; early alveolar exudation is not prominent, but the disease progresses rapidly [16].