To investigate the effect of dapagliflozin on clinical symptoms, quality of life, and differentiation of T lymphocyte subsets in patients with heart failure with reduced left ventricular ejection fraction (HFrEF). Methods 60 patients with HFrEF in our hospital from February 2019 to February 2022 were selected and divided into control groups (n=30) and study groups (n=30) according to the random number table method.The control group was given routine treatment, and the study group was assigned dapagliflozin treatment based on the control group. The clinical symptoms improvement effect, cardiac function indexes ［left ventricular end-diastolic diameter (LVEDD), left ventricular ejection fraction (LVEF) before and after treatment were compared between the two groups, left ventricular end-systolic diameter (LVESD)］, biochemical factor levels ［insulin-like growth factor 1 (IGF-1), N-terminal pro-B-type natriuretic peptide (NT-proBNP), homocysteine (Hcy)］, T lymphocyte subsets (CD3+, CD8+, CD4+/CD8+) differentiation and quality of life. Results The total effective rate of clinical symptom improvement in the study group was higher than that in the control group (P＜0.05). After 3 months of treatment, compared with the control group, the levels of LVEDD, LVESD, NT-proBNP, Hcy and CD8+ in the study group were lower (P＜0.05), and the levels of LVEF, IGF-1, CD3+ and CD4+/CD8+ in the study group were higher (P＜0.05). After 3 months of treatment, compared with the control group, the scores of physical domain, emotional domain and other domains in the study group were lower (P＜0.05). Conclusion Dapagliflozin can improve the clinical symptoms and cardiac function of patients with HFREF, regulate the expression levels of NT-proBNP, Hcy, and IGF-1, promote the balance of T lymphocyte subset differentiation, and improve the quality of life of patients