BACKGROUND: COVID-19 continuously threated public health heavily. Present study aimed to investigate the lymphocyte subset alterations with disease severity, imaging manifestation, and delayed hospitalization in COVID-19 patients. METHODS: Lymphocyte subsets was classified using flow cytometry with peripheral blood collected from 106 patients. RESULTS: Multivariate logistic regression showed that chest tightness, lymphocyte count, and gamma-glutamyl transpeptidase were the independent predictors for severe COVID-19. The T cell, CD4(+) T cell and B cell counts in severe patients were significantly lower than that in mild patients (p = 0.004, 0.003 and 0.046, respectively). Only the T cell count was gradually decreased with the increase of infiltrated quadrants of lesions in computed tomography (CT) (p = 0.043). The T cell, CD4(+) T cell, and CD8(+) T cell counts were gradually decreased with the increase of infiltrated area of the maximum lesion in CT (p = 0.002, 0.003, 0.028; respectively). For severe patients, the counts of T cell, CD4(+) T cell, CD8(+) T cell gradually decreased with the increased delayed hospitalization (p = 0.001, 0.03, and < 0.001, respectively). The proportions of T cell, CD8(+) T cell gradually decreased with the increased delayed hospitalization (both p < 0.001), but the proportions of NK cell, B cell gradually increased with the increased delayed hospitalization (p = 0.007, and 0.002, respectively). For mild patients, only the NK cell count was gradually decreased with the increased delayed hospitalization (p = 0.012). CONCLUSION: T lymphocyte and its subset negatively correlated with disease severity, CT manifestation and delayed hospitalization. The counts of lymphocyte subset were changed more profound than their proportions.