Although the understanding of the pathophysiological mechanism of sepsis has significantly improved, the outcome of septic patients remains poor. It is because of the heterogeneity of immune response, complex signaling pathways, the interplay of pro-inflammatory and anti-inflammatory processes and so on. Moreover, immunosuppression in sepsis increases the risk of death. Even survivors often remain a persistent immunosuppression status, which is one of the main reasons for long-term mortality. During pandemic of coronavirus disease 2019(COVID-19), severe COVID-19 patients also meet the diagnostic criteria of sepsis. In different periods of sepsis, there are close correlations between the counts of T cell subsets and immune status, demonstrated by monitoring peripheral helper T cells, regulatory T cells and CD8⁺T cells. The premise of appropriate treatment is to assess the patient's immune status precisely. Therefore, this review focuses on the change of T cell subsets counts, especially in patients with COVID-19, aiming to provide a monitoring indicator for precision immune treatment and improve outcome in sepsis.