Objective：To summarize the clinical experience，characteristics and progression of severe coronavirus disease 2019（COVID-19）. Methods：The epidemiological data，disease characteristics，treatment，clinical indexes，biochemical indexes and imaging characteristics of 13 patients with severe COVID-19 were retrospectively analyzed. Results：In severe COVID-19 patients，the lym－phocyte（LYM） count was significantly decreased in the early stage and further decreased in the advanced stage，while was increased in the remission period，but did not completely return to the normal value，with statistical differences in each period（F=15.396，P=0.000）. C-reactive protein（CRP） and inter－leukin-6（IL-6） were increased in the early stage，began to de－crease in the progression stage，and significantly decreased in the remission stage，with statistical differences between the re－mission stage and the early stage and the progression stage（CRP：F=5.366，P=0.009；IL-6：F=5.367，P=0.009）. Lactate dehydrogenase（LDH） and myoglobin（Mb） were significantly increased in the early stage，slightly decreased in the progressive stage and signifi－cantly decreased in the remission stage. LDH was statistically different in each stage（F=10.464，P=0.000），but Mb was only signifi－cantly different in the remission stage and early stage（F=4.303，P=0.021）. Creatine kinase（CK） was increased in the early stage，and decreased significantly in the advanced stage，and continued to decline in the remission stage，with statistical differences between the early stage and the advanced stage and the remission stage（F=3.782，P=0.032）. Albumin（ALB） was decreased in the early stage，and decreased obviously in the advanced stage，with a statistical difference between the early stage and the remission stage（F=5.264，P=0.010）. Oxygen index（OI） decreased in the early stage，and further decreased in the advanced stage，which was significantly different from the early stage and the remission stage（F=59.334，P=0.000）. Imaging features in the early stage，there were patches or flakes of ground glass shadow，thickening of bronchovascular bundle was able to be seen，partially thickening and consolidation of interlobular septum，which was mainly distributed under pleura. In the progressive stage：there are both patchy ground glass shadow and con－solidation，mainly mixed density，and consolidation range was increased. Thickening of interlobular septum and bronchiectasis was able to be seen，partially fibrofocus；the development trend of lesions was from peripheral to central and a few patients had complications of a small amount of pleural effusion. Few patients had problems that new lesions appeared after the absorption or decrease of early lesions. In the remission stage：the scope，number and density of lesions were reduced and the remaining were solid and fibrous foci. Conclusion：The most common abnormal biochemical indicators in patients with severe COVID-19 are decreased OI，decreased hypo-albuminemia，decreased LYM count，and elevated CRP，IL-6，LDH，CK and Mb. CRP，IL-6，LDH，CK and Mb are increased significantly at an early stage，and are sensitive to response. Instead of continuing to increase during the progression phase，they are declined，suggesting that early glucocorticoid and intervention therapy are effective. Although respiratory failure has not been corrected，the inflammation index has begun to decline，and the disease may develop for the better. In the remission period，the above indicators continues to decline，and the disease is improved. While the ALB and LYM counts continues to decline until the progression period，after the correction of respiratory failure，the recovery is slow，and the response is delayed. CT images of the chest have relatively distinctive manifes－tations，with main characteristics of exudation and ground glass lesions in the early period，and further increase and consolidation of exudation in the progressive stage. Few lesions have the phenomenon of ebb and flow，and the absorption of lesions in the remission stage is reduced，and fibrosis is formed.