Abstract： Objective To analyze the characteristics of peripheral blood T lymphocyte subsets in patients with no-vel coronavirus infection.Methods Data were collected from 78 patients with novel coronavirus infection,who underwent T lymphocyte subset testing during hospitalization.A retrospective analysis was performed on the trends of T lymphocyte subsets in the two weeks following the first positive nucleic acid test.Clinical characteristics were compared between the group with a decreased CD4/CD8 ratio and the normal group.Results A total of 84 tests were conducted on 78 patients with novel coronavirus infection,with an average age of(70.81±16.29)years.Among them,53(67.95％)were elder-ly patients,53(67.95％)were male,and 22(28.21％)were unvaccinated against novel coronavirus infection.The me-dian number of days from symptom onset to hospitalization was 5(IQR:2.0,8.5).In the early phase(0-14 days)of novel coronavirus infection,the absolute counts of total lymphocytes,total T lymphocytes,helper T cells,and cytotoxic T cells were all below normal values.The CD4/CD8 ratio was 1.20(IQR:0.89,2.00)in the DO-1 period and 2.67(IQR:1.75,3.37)in the D8-14 period.Univariate analysis indicated that a decreased CD4/CD8 ratio was associated with the severity of the disease and the timing of peripheral blood T lymphocyte subset testing(P＜0.05).Conclusion In patients with novel coronavirus infection,peripheral blood T lymphocyte subsets generally show a declining trend.A de-creased CD4/CD8 ratio is associated with the severity of the disease and the timing of lymphocyte testing following the di-agnosis of novel coronavirus infection.