Abstract: Objective The purpose of this study was to evaluate whether 99mTc-HL91 hypoxia imagining could forcast the radiosensitization effect of hyperbaric oxygenation to tumor. Methods Forty bearing H22 tumor mices were divided to 4 groups, 10mices/group: ① The control group: 5 mices to carry on 99mTc-HL91 hypoxia imaging, the remained 5 mices to perform radiotherapy;② The 15 minute group;③ The 30 minute group;④ The 60 minute group. The behind three groups 5 mices to carry on 99mTc-HL91 hypoxia imaging, the remained 5 mices to perform radiotherapy according to the different order after hyperbaric oxygen.ROI were drawn around tumor and contralateral muscles in planar images to calculate the T/NT all of imaging mices. The mices were killed immediately after image acquisition, then the tumors were excised,weighted and the radioactivity were measured. Differential uptake ratio(DUR) was computed to quantitate the tracer uptake. Every radiotherapy group mices were observed and recorded the time of the tumors growth and the average survival time of the mices.Results Compared with the control group, the DUR 、T/NT and the delay times of the tumors growth and the mices,the15min group and 30min group suggested significant difference （P<0.05）, 60min group suggested no significant difference（P>0.05）.Conclusion 99mTc-HL91 hypoxia imaging is an effective forecasting effects of hyperbaric oxygen enhancement methods, and the sensitizing effect of hyperbaric oxygen decreased gradually with time.