Abstract: 【Objective】The effects of hypoxia and reoxygenation on intestinal tissue structure,energy metabolism and microbial flora of Onchidium reveesii were analyzed,and the mechanism of hypoxic stress resistance and reoxygenation recovery was explored,so as to provide a theoretical reference for the study of stress resistance and recovery mechanism of intertidal organisms. 【Method】Normal oxygen group(control group), hypoxia group and reoxygenation group were set up respectively. After 4,8,12 and 24 h of hypoxic stress and reoxygenation 6,12,18,30 and 42 h, the changes of intestinal tissue structure of O. reveesii were observed,the lactate content,lactate dehydrogenase(LDH) and acid phosphatase(ACP) activities were measured,and the changes of intestinal microbial flora were analyzed. 【Result】With the prolongation of hypoxic stress,the number of goblet cells in the intestinal tissue of O. reveesii increased significantly,and the goblet cells were almost all over the epithelial layer at 24 h,and gradually returned to normal after reoxygenation. The lactate content of intestinal tissues increased with the prolongation of hypoxia stress,LDH activity showed an up-down variation,reaching the highest values at 24 and 12 h of stress respectively,and there were significant differences between them and the control group(P<0.05,the same below),while the activity of ACP increased first,then decreased and then increased,and decreased to the lowest value at 8 h,which was significantly lower than that of the control group. After reoxygenation,lactate content,LDH activity and ACP activity were restored. The structure and relative abundance of intestinal microbial flora structure changed due to hypoxic conditions,and the dominant microbial flora changed from Firmicutes in the control group to Proteobacteria,Actinobacteria and Campylobacterota at phylum level. At the genus level,the dominant colony changed from Aeromonas to Vibrio,and Firmicutes regained their dominant position after reoxygenation. Although the relative abundance of colonies rebounded after reoxygenation,the overall abundance of colonies was still lower than that of the control group. LEfSe analysis results showed that there were 20 significant difference communities between the control group and the hypoxic 8 h group, mainly concentrated in Endozoicomonas and Vibrio. There were 39 significant differences between the control group and the reoxygenation group, mainly concentrated in Flavobacteriaceae and Helicobacteriaceae. 【Conclusion】Hypoxia affects the intestinal tissue structure of O. reveesii,resulting in changes in intestinal flora,which in turn affects the antioxidant function and non-specific immune function of the intestine.