Abstract： Objective:To provide references for finding an objective, accurate, highly repeatable and operable measurement method of the resting energy expenditure (REE) for flying personnel by taking the indirect calorimetry measured REE as the gold standard and establishing the formula for predicting REE combined with body composition indexes.Methods:Fourteen normal-size male volunteers were chosen as the subjects. The hypobaric hypoxia environment was constructed in the hypobaric chamber. The subjects were asked to complete single task (flight control) and dual task (flight control and calculation). The body weight, fat free mass (FFM), muscle mass (MM), fat mass (FM), waist-to-hip ratio (WHR), visceral fat mass (VFM) and body fat percentage (BF%) were directly measured by body composition analyzer. The respiratory frequency (RF), volume of CO 2 (VCO 2), maximal volume of O 2 (VO 2max), volume of tidal (VT), minute ventilation volume (VE), metablic equivalent (MET), REE and REE/kg/d were measured by gas metabolizer. The correlation between REE and body composition indexes was analyzed and a linear regression equation was obtained. Results:In the simulated hypobaric hypoxia environment, the RF, VCO 2, VO 2max, VE, VT, REE, REE/kg/d, MET and heart rate of the subjects increased slightly in the dual task, but there were no significant differences between the dual task and the single task (all P>0.05). REE was positively correlated with FFM and MM ( r=0.566, 0.570, P=0.035, 0.033), but not with height, FM and heart rate (all P>0.05). The prediction formula of REE in hypobaric hypoxia environment was Model A: REE=60.34×MM-1 121 ( r=0.570, P=0.033), or Model B: REE=55.34×FFM-1 073 ( r=0.566, P=0.035). There was a positive correlation between the predicted REE and the measured REE ( r=0.570, P=0.033) for Model A, and the error value was (0.032±358.170) kcal/d, P=1.00>0.05. Conclusions:FFM and MM are the main determinants of REE in normal-size subjects under hypobaric hypoxia environment. Either MM or FFM shows a good prediction effect to REE.