objective: To observe the apoptosis of splenic T cells and the expression of XAF1, FAS and TNF-α proteins in rats with acute lung injury (ALI), and to investigate whether the mechanism of protection against ALI by Yifei Jianpi Formula is related to the down-regulation of the expression of XAF1, FAS and TNF-α proteins, and the inhibition of T cell apoptosis.Methods: Sixty male SD rats of SPF grade were randomly divided into blank group, model group, positive group, and high, medium and low dose groups of Yifei Jianpi Formula. The positive group was given 0.5 g/kg dexamethasone by gavage, the high, medium and low dose groups of Yifei Jianpi Formula were given 12, 6 and 3 g/kg of Yifei Jianpi Formula by gavage, respectively, and the model group and the blank group were given equal amounts of saline by gavage, and the medication was administered once a day for 14d.The lung function of the rats in each group was detected by the animal lung function testing system, We observed the imaging characteristics of the lungs and changes in organ index and wet/dry weight (W/D) of lung tissues in each group of rats; hematoxylin-eosin (HE) staining was used to observe the pathological changes of lung tissues in each group; flow cytometry was used to detect the splenic T-cell subpopulations (CD4₊^/CD₊8) and apoptosis of splenic T-cells in each group of rats and the Western blot technique was used to detect the levels of XAF1, FAS and TNF-α protein expression levels in the spleen.Results: The rats in the model group had reduced lung function, decreased spleen and thymus organ index, and significantly higher wet/dry weight (W/D) of lung tissue (P<0.01), Inflammatory exudation and alveolar rupture in the lung tissue, accompanied by thickening of the lung texture and large areas of ground-glass shadows, with a significant decrease in T-cell subsets (CD4₊^/CD₊8), and a significant increase in the expression of XAF1, FAS, and TNF-α proteins as well as in the rate of apoptosis of T-cells (P<0.01) After the intervention of the Yifei Jianpi Formula, the wet weight/dry weight (W/D) spleen of rat lung tissues was significantly reduced, the organ index of the thymus was significantly increased (P<0.05,P<0.01), the T-cell subpopulation (CD4₊^/CD₊8) was significantly increased, and the protein expression of XAF1, FAS, and TNF-α as well as the apoptosis rate of T-cells were significantly decreased (P<0.05,P<0.01)..Conclusion: ALI induced up-regulation of XAF1, FAS, and TNF-α protein expression and T-cell apoptosis in the spleen of rats, and Yifei Jianpi formula may protect against ALI by down-regulating XAF1, FAS, and TNF-α protein expression and inhibiting apoptosis of splenic T-cells.