OBJECTIVE: To observe the influences of intermittent normobaric hypoxia (INH) training on heart rate variability (HRV) under hypoxia. METHOD: Eight subjects were trained with INH for 4 weeks (24 d), subjects\' HRV level, recorded during exposure to hypoxia (10% O2) before and after the training, were compared and analyzed. RESULT: After the INH training, average of normal to normal Intervals (R-R), standard deviation of normal to normal Intervals (SDNN), total power (TP), high frequency (HF) and low frequency (LF) increased significantly during hypoxia (P<0.05 - P<0.001); normalized low frequency (LFn), normalized high frequency (HFn) and LF/HF showed no significant change. CONCLUSION: 1) INH training can increase subjects\' HRV under hypoxia; 2) INH training can not only be used to increase the tolerance of hypoxia, but it is also good for increasing astronaut\'s flying tolerance under special environment.