Background: Ever since the COVID-19 pneumonia emerged in Wuhan, China, in December 2019, it has rapidly spread worldwide, resulting in high mortality. This study aimed to delineate the clinical characteristics of critically ill patients with COVID-19 infection in the intensive care unit. Methods: In this retrospective study, the clinical characteristics of 88 critically ill patients with COVID-19 infection were collected. Analysis among three subgroups, classified according to the survival time, was performed. Results: The median age was 70.7(62.3-78.25) years of critical ill patients. Hypertension (43.2%) was the most frequent underlying disease. At the time of admission, compared to other patients, patients of the≤7 days category showed greater impairment of consciousness, as per the Glasgow Coma Scale (GCS) scores(11.0±2.9, P<0.01). The lymphocyte percentages in all patients (4.1 ± 0.78) were much lower than the normal values. Particularly, acute kidney failure occurred more frequently in patients of the ≤7 days category (45.2%, P<0.01). The time distributions of the mortality rates were 31deaths in ≤7 days, 33 deaths in 8–14days, and7 deaths in >14days (P=0.01). Conclusion: Critically ill patients with COVID-19 infection showed high risk of mortality. The primary immune response of lymphocytes against the COVID-19 infection was severely destroyed. Higher GCS score predicted greater possibility of survival. However, acute kidney injury may be an indicator of worse outcome.