Objective      To determine the effect of short-term simulated microgravity on man′s ability in object mental rotation test.        Methods      Sixteen healthy subjects volunteered to participate in a 72-hour head down tilt bed rest (HDT) test

and accomplished stimulate mental rotation tests with letter “F” pictures as stimulation

in 1 d before the HDT (HDT/0D) and in continuous 3 d after HDT (HDT/1D

HDT/2D

HDT/3D) respectively

. The behavior and event related potential (ERP) data were collected and analyzed.        Results      Significant linear relationship was found in the rotation angle of stimulation pictures with the response time. From the HDT/0D to HDT/3D

the linear fitting intercept of mental rotation time was changed with angle but without statistically significance[F（3

45）=1.216

P

=0.309

]

and the fitting of slope also had no statistically significance[F（3

45）=0.235

P

=0.817

]

. ERP results indicated that the main effect of rotation angle reached statistically significant [F（3

45）=44.478

P

0.01

]

. The average amplitude of P300 among 4 angles had significant differences (

P

0.05). Main effect of HDT time factor reached statistically significant [F（3

45）=6.585

P

=0.004

]

and average amplitude between HDT/1D and HDT/0D had significant difference

but there was no statistical difference at other time points.        Conclusion      Simulated weightlessness does not change the process of individual mental rotation

and the greater of the rotation angle is

the longer the reaction time is

and the more psychological resources it requires. After HDT

individuals’ mental rotation capacity falls first and then recovers

indicating that brain function has an adaptive change under physiological effect of weightlessness.