In studies of recognition retrieval, emotional memory enhancement effect was described as better memory performance for emotional stimuli than neutral ones. Based on dual-processing theory, recognition retrieval can be divided into two different processes: familiarity and recollection. Two important event-related potential correlates, the FN400 (a negative shift in frontal regions at 300~500ms time window), and the late positive complex (LPC; a positive peak over posterior regions at 500~800ms time window) was associated with familiarity and recollection, respectively. Some researchers considered that emotional memory enhancement effect occurred in recollection but not in familiarity. However, some indirect evidences showed that emotion could enhance memory strength in familiarity-based retrieval. Our research focused on two controversies: 1) whether emotion can enhance familiarity, and 2) how arouse and valence of emotion affect memory enhancement effect. In the current experiment, we used modified “remember/know” paradigm with ERPs recorded, to investigate how emotion influences familiarity and recollection in long-term study-test duration. Subjects were instructed to learn the pictures (including neutral, negative and positive pictures). And after one week, they made “remember/know/guess/new” recognition judgments towards stimuli intermixed with learnt and new pictures. Finally, the valence and arouse of experimental pictures were evaluated by the subjects participated in the experiment. Behaviorally, for studied pictures endorsed as “know”, the memory performances of emotional pictures were better than neutral ones, and there was no significant difference between emotional valences. As for the “remember” judgments, the memory performances of negative pictures were better than positive and neutral ones. ERP results show that, for the pictures judged as “know”, the FN400 old/new effects were significant in emotion condition but not in neutral condition, suggesting that emotion arousing enhanced familiarity-based retrieval. For pictures judged as “remember”, the LPC potentials of negative pictures were more positive than positive and neutral ones, showing that emotion valence modulated recollection-based retrieval. Our findings suggest that: in long-term study-test duration, emotional pictures could result in memory enhancement effect in the familiarity-based as well as the recollection-based retrieval. The emotional memory enhancement effect was not only modulated by the arousing as well as the valence of emotion. Emotional arousing played a predominant role in enhancing memory strength for familiarity-based retrieval. Emotional valence exerts influence exclusively on recollection-based retrieval in a way that only negative pictures could make enhancement effect on recollection.