AIM:To observe the influence of head down tilt simulated weightlessness on electrophysiology of vision. ·METHODS:Head-down tilt for -6° was adopted in 6 healthy volunteers. Pattern visual evoked potential (P-VEP) under different space frequency,flash electroretino-graphy (ERG),including rod response,maximal res-ponse,cone response,oscillatory potentials (OPs) and 30Hz flicker were recorded,and the latency and amplitude from each wave were analyzed before,two days and five days after trial. The record procedure followed the ISCEV standard for full-field clinical ERG (2008 update). ·RESULTS:No significant difference was detected in the latencies of P100 under different space frequency. The amplitude of P100 had significant change under high space frequency between pre-test and 2,5 days after test (P<0.05). But not the same happened in middle and low space frequency. No significant differences were detected in the latencies and amplitudes of cone response and 30 Hz flicker among various time points(P>0.05). The latencies were significantly prolonged in rod and maximal responses between pre-test and 2 days after test (P<0.05),but no obvious change was found in amplitudes(P>0.05). There were no significant differences detected in the ∑OPs (P>0.05). ·CONCLUSION:Head-down tilt simulated weightlessness induce the abnormality of VEP and ERG which influence the visual function of healthy people.