Objective To study the qi-tonifying effect and mechanism of different polar parts of water extract of Cinnamomum cassia branches and leaves on qi-deficiency rats, and to provide reference for the pharmacodynamic material basis of Cinnamomum cassia qi-tonifying. Methods Ninety Wistar male rats were randomly divided into blank group, amodel group, positive 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, Water fraction low dose group, with 10 rats in each group. Except for the blank group, the other groups used the ' improper diet + fatigue ' method to construct the animal model of qi deficiency. At the same time of modeling, the rats were given intragastric administration once a day for 21 days. After the last administration, the body weight and weight-bearing swimming time of the rats were recorded. Anti-tumor necrosis factor-alpha ( TNF-α ), interleukin-2 ( IL-2 ), interleukin-12 ( IL-12 ), creatine kinase ( CK ), lactic acid ( LD ), lactic dehydrogenase ( LDH ), superoxide dismutase ( SOD ), malondialdehyde ( MDA ), albumin ( ALB ) in serum and adenosine diphosphate ( ADP ), adenosine triphosphate ( ATP ) in liver were measured. The thymus index, spleen index and liver index were measured, and the liver of each group was observed by HE staining. Results Compared with the model group, the qi deficiency symptoms and liver tissue damage of the rats in each administration group were improved to varying degrees. The ethyl acetate fraction and n-butanol fraction could significantly prolong the weight-bearing swimming time of Qi deficiency rats ( P < 0.01 ). The high dose of ethyl acetate extract could significantly increase the thymus index, TNF-α, IL-2, IL-12, ADP, ATP, SOD and ALB contents ( P < 0.05, P < 0.01 ), and significantly reduce the contents of CK, LD, LDH and MDA ( P < 0.05, P < 0.01 ). The low dose of ethyl acetate fraction could significantly increase the contents of IL-2, ATP, ADP and ALB ( P < 0.05, P < 0.01 ), and significantly reduce the contents of MDA, LD and LDH ( P < 0.05, P < 0.01 ). The high dose of n-butanol fraction could significantly increase the thymus index, IL-2, IL-12, ATP, ADP, ALB and SOD contents ( P < 0.01 ), and significantly reduce the contents of TNF-α, CK, LD, LDH and MDA ( P < 0.05, P < 0.01 ). The low dose of n-butanol fraction could significantly increase the contents of SOD, IL-1, ALB, ATP and ADP ( P < 0.05, P < 0.05 ). Conclusion The different polar parts of the water extract of Cinnamomum cassia branches and leaves can improve the symptoms of qi deficiency in rats to varying degrees and protect the thymus, spleen and liver of qi deficiency rats, and can regulate the levels of various factors in qi deficiency rats, thereby improving their immunity and reducing organ damage. Various effects such as qi supplementation, prolonging the time of fatigue, and enhancing the body 's exercise endurance.