Abstract: ［Abstract］Objective To investigate the effect of different time of hypoxia reoxygenation （HR） on cell autophagy and cell viability．Methods　According to the different reoxygenation time， H9C2 cells were divided into five groups: normal control group（group A）， hypoxia group （group B）， reoxygen 2h group （group C）， reoxygen 12h group（group D）and reoxygen 24h group （group E）. The expression of LC3 II/LC3 I in each groups was detected by Western Blot，and the activity of myocardial cells was detected by MTT. Results　MTT results showed that the viability of the myocardial cells after hypoxia 2h/reoxygenation 2h was significantly lower than that in the normal control group（P＜0.05）. The ratio of LC3 II/LC3 I of the cells in group B （hypoxia group）， group C （reoxygen 2h group）， group D （reoxygen 12h group）， group E （reoxygen 24h group） was significantly higher than that of group A （normal control group） （P＜0.05）. Among them， the ratio of LC3 II/LC3 I of the cells in group C and D were significantly higher than that of group B（P＜0.05）， paticlularly the group D was the highest （P＜0.05） .The activity of myocardial cells in group D was the lowest among all groups. Conclusion　Culturing in the three gas incubator can obviously decrease the viability of H9C2cells. Hypoxia can activate autophagy， and autophagy increases significantly after reoxygenation. Autophagy may be activated most obviously at 12 hours and decrease to the level of hypoxia group at 24 hours. Cells can be damaged by hypoxia， and further increase of cellular damage may occur after oxygen inhalation. At 12 hours，the cell viability is the lowest， and the cell viability may be improved at 24h.