Objective Observe the impact of Qang Gu Kang Wei extraction(KW)on skeletal muscle atrophy in simulated weightlessness rats by regulating endoplasmic reticulum stress and mitochondrial fusion.Methods SD rats were randomy divided the control group(Control),the simulated weightlessness group(TS),and the KW group(TS+KW).Rats were treated with KW with or without tail suspension(TS)for 28 days,and the cross-sectional areas of the gastrocnemius muscle were compared with a control group.The expression levels of endoplasmic reticulum stress(ERS)and key proteins involved in mitochondrial fusion were also analyzed.Results KW treatment reduced the loss of muscle cross-sectional area caused by TS.TS increased the protein expression of glucose-regulated Protein 78(GRP78)and components of the ERS signaling pathways,while KW treatment reduced this increase.TS also inhibited the expression of mitofusin 2(MFN2),which was increased by KW treatment.Additionally,KW treatment promoted the interaction between GRP78 and the endoplasmic reticulum protein sigma-1 receptor(Sig-1R).Conclusion KW may attenuate muscle atrophy caused by simulated weightlessness by regulating ERS and mitochondrial fusion fusion.