The results of this study showed that DD and Fg could be used as new indicators for the clinical classification of COVID-19. In the first test of DD, 50 of 115 patients had abnormal levels of DD (>0.55 mg/L), accounting for 43.5% (50/115). Of the 28 critically ill patients, 17 were >0.55 mg/L, accounting for 60.7%. (17/25), and 14 cases had two times more than the normal reference value. 70.4% (81/115) of the COVID-19 patients had abnormal concentration of Fg. Additionally, it is noticed that the level of Fg was significantly increased in severe and critically ill patients, with 70.3% of severe and critical patients (52/74) >4.00 g/L. The results of the study indicate that the levels of DD and Fg significantly increased in severe and critically ill patients, and some patients deteriorated during treatment, suggesting that COVID-19 patients, especially severe patients, have a high risk of thrombosis, which is consistent with previous reports [1, 4].