Objective To investigate the clinical characteristics and test results of the elderly patients with coronavirus disease 2019 so as to provide reference for their diagnosis and treatment. Methods A retrospective analysis was conducted of the clinical data of 73 COVID-19 inpatients over 80 years old treated in the Cadre′s Ward of First Affiliated Hospital of Naval Medical University from December 7 to December 31,2022. According to COVID-19 Diagnosis and Treatment Protocol(9^th Trial Version),the patients were divided into the light and medium group (n=34) and the severe and critical group (n=39).The test results on admission and 48 h later were compared. SPSS statistics 26.0 was used for data analysis. Data comparison between two groups was performed using t test, Mann-Whitney U test orχ² test depending on the data type. Multivariate logistic regression was employed to analyze the independent risk factors for the severe and critical COVID-19 in the elderly. Results The severe and critical group had longer pre-hospital home treatment and larger number of underlying comorbid chronic diseases but lower saturation of blood oxygen (SpO₂) without oxygen inhalation than the light and medium group, the differences being statistally significant (P＜0.05). Lymphocyte count, lymphocyte percentage, albumin, glomeruar filtration rate(GFR), SpO₂ and partial pressure of oxygen (PO₂) in the severe and critical group were lower than those in the light and medium group, and fibrinogen, D-dimer, creatinine, urea nitrogen and lactate dehydrogenase in the former were higher than those in the latter, and the differences were statistically significant. Logistic regression analysis showed that the pre-hospital home treatment time (OR=0.265,95%CI 0.085-0.830) and SpO₂ without oxygen inhalation (OR=1.717,95%CI 1.016-2.901) were the independent risk factors of the severe and critical COVID-19 infection in the elderly. Conclusion The elderly with long pre-hospital treatment and low SpO₂ without oxygen inhalation are the high-risk groups for severe or critical COVID-19 infection. Attention should be paid to the changes in lymphocyte count and percentage, coagulation, liver and kidney function, myocardial zymogram, arterial blood gas analysis and other indicators, and intervetion should be taken as soon as possible to improve the prognosis.