Objective      To investigate the features and related factors of brain function in long staying soldiers at high altitude.       Methods      Sixty-four male soldiers living at the plain and 65 soldiers living at 4 500 m altitude for 1-15 years were enrolled in this study. The neurobehavioral core tests battery (NCTB) and Raven’s standard progressive matrices (RSPM) test were adopted to evaluate cognitive capacity. The sleep qualit

y was investigated using Pittsburgh sleep quality index (PSQI). Meanwhile

the resting oxyhemoglobin saturation (SaO

2

) and the brain tissue oxygenation index (TOI) were also measured.       Results      The brain TOI of the soldiers living at 4 500 m altitude decreased significantly (P0.01) and was positively correlated with SaO

2

(

r

=0.364). They were more fallible on color discrimination (

P

0.01)

were slower on reaction to blue color stimulus (

P

0.05)

and exhibited significantly worse emotions (

P

0.05) and performance on visual retention (

P

0.01) and motor stability (

P

0.05). Except for a negative correlation between PSQI and brain TOI (r=-0.287)

no other decreasing brain function was associated with reduced brain oxygen supply. The color reaction time and visual retention were associated with residence time at high altitude (

r

=0.268

r

=-0.277).       Conclusion      Chronic hypoxic exposure at high altitude has a profound effect on the negative effect on the visual function

motion stability

emotion and sleep quality. Brain TOI and residence time are influencing factors of impaired brain function at high altitude.