Abstract: Startle reflex(SR), as a kind of protective reflex by animals and human beings to avoid potential dangers in the exposure to unexpected stimulus or dangerous conditions, has its biological significances. Most of the previous studies focused on acoustic startle reflex, and adopted the reflexes of eyes and facial expression muscles, like eyeblink reflex, as the dependent variable. The physiological mechanism of SR is the direct pathway through amygdale. While the psychological mechanism of strengthened SR is sensitization or fear-conditioning that of weakened SR is habituation, prepulse inhibition or pleasure-attenuation. Future studies should pay more attention to visual startle reflex. The reflex pattern of the gesture-holding muscles throughout the body is to be observed, and more in-depth studies are to be carried out, with the help of advanced instruments, on the brain’s information processing mechanism for startle reflex

Key words: startle reflex, reflex index, physiopsychological mechanism