Abstract: Posttraumatic stress disorder is a kind of anxiety disorder which developed after severe trauma. The key of treatment for this disorder is to extinct the conditioned fear memory acquired in trauma. But the most effective exposure therapy can’t repress fear memory efficiently. Researches from animal model of fear conditioning showed that: enhancing effects of emotional arousal, secondary-order conditioning and reconsolidation of fear memory, deficient function of medial prefrontal cortex etc all are reasons block the extinction of fear memory. According to these reasons，corresponding treatment ways can be explored and developed

Key words: conditioned fear memory, extinction, emotional enhancing effect, secondary-order conditioning, reconsolidation, medial prefrontal cortex