Abstract: Objective: To explore the protective mechanism of Xiaoshi Xionghuang San on vascular endothelial cell hypoxia injury.Methods: Griess method was used to detect the content of nitrate (NO₃^-) and nitrite (NO₂^-) in Chinese medicine Xiaoshi (XS), Xionghuang (XH), and Xiaoshi Xionghuang San (XSXH), and the level of serum nitric oxide (NO) in mice of each group.Mouse serum of each component of Xiaoshi Xionghuang San was prepared and human coronary crtery endothelial cells (HCAEC) were divided into Blank, Hypoxia, Hypoxia+XS, Hypoxia+XH and Hypoxia+XSXH groups.Blank group was treated with normoxia, and the other groups were given hypoxia for 24 h to prepare cell hypoxia models.Serum of mice was used to intervene HCAEC; tetramethylrhodamine (TMRM) and mitochondrial superoxide indicator (MitoSOX) were used to detect mitochondrial membrane potential and reactive oxygen species (ROS) levels of HCAEC in each group.The levels of nitric oxide (NO) in HCAEC of each group were detected by Griess and the levels of ET-1 and IL-6 and TNF-α were detected by ELISA.Results: The content of NO₂^- in XSXH group was higher than that in XS group and the content of NO₃^-was lower than that in XS group (P＜ 0.001), and the content of NO₃^- and NO₂^- was the lowest in XH group (P＜ 0.001, P＜ 0.01).Compared with Blank group, levels of serum NO of mice in XS group, XH group and XSXH group increased (P＜ 0.05, P＜ 0.01, P＜ 0.001).Cell results showed that Hypoxia group could significantly reduce the biological activity of NO in cells, increase the levels of ET-1 and inflammatory factors (IL-6, TNF-α), decrease mitochondrial membrane potential and generate a large number of ROS (P＜ 0.001).Compared with Hypoxia group, the above indicators in the Hypoxia+XS, Hypoxia+XH and Hypoxia+XSXH groups significantly improved (P＜ 0.05, P＜ 0.01, P＜ 0.001), of which the Hypoxia+XSXH group had the strongest effect and the Hypoxia+XS group was stronger than the Hypoxia+XH group (P＜ 0.05).Conclusion: XS, XH and XSXH can all increase the biological activity of NO to varying degrees and protect the hypoxia injury of vascular endothelial cells by reducing the levels of ET-1 and inflammatory factors, restoring mitochondrial membrane potential and reducing the generation of ROS, among which XSXH has the strongest effect.