Objective: To understand the differences in lymphocyte subsets in patients with different clinical classifications of corona virus disease 19 (COVID-19). Methods: Eighty-one patients with COVID-19 who were admitted to the isolation ward under the responsibility of three medical aid teams in the Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, from February 8, 2020 to March 28, 2020, were selected to collect clinical data. According to the relevant diagnostic criteria, the disease status of the patients was classified into moderate cases (n=35), severe cases (n=39) and critical cases (n=7) when lymphocyte subset testing was performed. Their blood routine tests, lymphocyte subsets and other indicators were tested to compare whether there were differences in each indicator between the patients of different clinical classification groups. Results: The differences in the absolute count of total lymphocytes, T-lymphocytes, CD4⁺T-lymphocytes, CD8⁺T-lymphocytes and natural killer (NK) cells among the three groups of patients were all statistically significant (P<0.05), and the critical cases were significantly lower than the moderate and severe cases in the above indicators, and the indicators showed a decreasing trend with the severity of the disease. In 22 patients, the six indicators of the absolute count of T-lymphocytes, B-lymphocytes, CD4⁺T-lymphocytes, CD8⁺T-lymphocytes and NK cells, CD4⁺/CD8⁺ ratio were all within the normal reference range in the first test, and 59 patients had abnormalities of the above indicators, with the absolute count of NK cells and CD8⁺ T lymphocytes decreasing most frequently (61%, 56%). The patients with the absolute count of NK cells and CD8⁺ T lymphocytes below the normal reference range were one group, and the remaining abnormal patients were the other group. There were more critical cases in the former group (moderate:severe:critical cases were 4:8:7 vs. 19:21:0, respectively, P=0.001), and all the deaths were in this group (6 cases vs. 0 case, P=0.001). The absolute B lymphocyte count was below the normal reference range in 15 patients, and the remaining 64 cases were within the normal range. The ratio of moderate, severe and critical cases in the reduced group was 4:7:4, and the ratio of critical cases was more in normal group which was 30:31:3, and the difference between the two groups was statistically significant (P=0.043). Conclusion: The more critical the clinical subtype of patients with COVID-19, the lower the absolute count of each subset of lymphocytes.