ObjectiveTo establish and evaluate a mouse model of heart failure with Qi deficiency syndrome. MethodForty-four KM mice were randomly divided into sham operation group， model group， and modified Si Junzitang group （12.89 g·kg^-1）. The model group and the modified Si Junzitang group underwent thoracic aortic constriction （TAC）， while the sham operation group only underwent suture without constriction. Echocardiography and pathological examination were used to assess the heart failure model and evaluate the pharmacological effects. Macroscopic characterization， microscopic biology， and formula identification were conducted to collect general signs， body weight， open-field behavior， grip strength， mitochondrial ultrastructure， and other macroscopic and microscopic characteristics of mice. Mitochondrial fission and fusion protein expression were measured to determine the syndrome type. ResultEight weeks after TAC， compared with the sham operation group， the model group showed a significant decrease in left ventricular ejection fraction （LVEF） （P<0.01）， and modified Si Junzitang improved LVEF in mice （P<0.05）. Hematoxylin-eosin （HE） staining of the heart showed inflammatory cell infiltration and thickening of blood vessel walls in the model group， which was significantly improved by modified Si Junzitang. After 6-8 weeks， compared with the sham operation group and the modified Si Junzitang group， the model group exhibited significant hair loss， hair yellowing， decreased activity， and depression. Moreover， compared with the sham operation group， the model group had a significantly lower increase in body weight （P<0.05）， while the modified Si Junzitang group showed a significant increase in body weight （P<0.05） compared with the model group. After 6-8 weeks， compared with the sham operation group， the model group showed a significant decrease in open-field distance and speed （P<0.05）， while the modified Si Junzitang group exhibited significantly improved open-field distance and speed in the 8^th week （P<0.05）. After 6-8 weeks， compared with the sham operation group， the model group exhibited a significant decrease in maximum grip strength （P<0.05）， while the modified Si Junzitang group showed a significant increase in maximum grip strength 8 weeks after TAC （P<0.05）. Transmission electron microscopy of the gastrocnemius muscle showed uneven muscle tissue matrix， mitochondrial swelling， increased volume， matrix dissolution， ridge loss， and vacuolization in the model group， while modified Si Junzitang improved mitochondrial swelling， ridge fracture， and matrix vacuolization. Western blot analysis showed that the expression of the kinetic associated protein 1 （DRP1） in the gastrocnemius muscle of the model group significantly increased （P<0.01）， and the expression of mitochondrial fusion hormone 1 （MFN1） significantly decreased （P<0.05） as compared with those in the sham operation group. Furthermore， compared with the model group， the modified Si Junzitang group exhibited a significant decrease in the expression of DRP1 （P<0.05） and a significant increase in MFN1 expression （P<0.01）. ConclusionMice exhibited significant manifestations of qi deficiency syndrome 6-8 weeks after TAC， accompanied by abnormal mitochondrial morphology and function in the gastrocnemius muscle， which were significantly improved by modified Si Junzitang.