Objective To study the qi-tonifying effects and mechanisms of different polar fractions of aqueous extract of Cinnamomum cassia branches and leaves in qi-deficiency rats, and to provide a reference for the pharmacodynamic material basis of Cinnamomum cassia qi-tonifying. Methods Ninety male SD rats were divided randomly into blank group, model group, positive group, aclministration group ( ethyl acetate fraction high dose group, ethyl acetate fraction low dose group, n-butanol fraction high dose group, n-butanol fraction low dose group,water fraction high dose group and water fraction low dose group) ( n= 10 rats per group). Except for the blank group, rats in the other groups were subjected to the “improper diet + fatigue” method to construct an animal model of qi deficiency. At the same time, rats were administered the fractions intragastrically once a day for 21 d. The body mass and weight-bearing swimming time were recorded after the last administration. Tumor necrosis factor-alpha (TNF-α), interleukin ( IL)-2, IL-12, creatine kinase ( CK), lactic acid ( LD), lactic dehydrogenase ( LDH),superoxide dismutase (SOD), malondialdehyde (MDA), and albumin (ALB) in serum, and adenosine diphosphate (ADP) and adenosine triphosphate ( ATP ) in liver were measured. Thymus, spleen, and liver indexes were measured, and the livers were observed by hematoxylin-eosin(HE) staining. Results Compared with the findings in the model group, qi-deficiency symptoms and liver tissue damage were improved in each administration group to different degrees. The ethyl acetate and n-butanol fractions significantly prolonged the weight-bearing swimming time in qi-deficient rats (P<0. 01). The high-dose ethyl acetate fraction significantly increased the thymus index and significantly improved TNF-α, IL-2, IL-12, CK, LD, LDH, SOD, MDA, ALB, ATP, and ADP levels (P<0. 05,P<0. 01), while the low-dose fraction significantly improved IL-2, LD, LDH, MDA, ALB, ATP, and ADP levels (P<0. 05, P<0. 01). The high-dose n-butanol fraction significantly increased the thymus index and significantly improved TNF-α, IL-2, IL-12, CK, LD, LDH, SOD, MDA, ALB, ATP, and ADP levels (P<0. 05, P<0. 01),and the low-dose fraction significantly improved IL-12, CK, LD, LDH, SOD, MDA, ALB, ATP, and ADP levels (P<0. 05, P<0. 01). The high-dose water fraction significantly improved IL-12, LD, LDH, MDA, and ATP levels ( P<0. 05, P<0. 01), while the low-dose fraction significantly improved LD levels ( P<0. 05 ). Conclusions Different polar fractions of the aqueous extract of Cinnamomum cassia branches and leaves can improve the symptoms of qi deficiency in rats to varying degrees. They can protect the thymus, spleen, and liver and regulate the levels of various factors in qi-deficiency rats, thereby improving their immunity and reducing organ damage.Through various effects such as qi supplementation, prolonging the time of fatigue, and enhancing the body’s exercise endurance, comprehensive indexes showed that the n-butanol fraction of the aqueous extract of Cinnamomum cassia branches and leaves had the greatest qi-invigorating effect.