Based on references in the scientific literature, empathy, the capacity to understand, share and evaluate others’ feelings and thoughts, plays a crucial role in human social communication and interaction. It has been proposed to mediate acquisition of appropriate social behaviors such as helping and cooperation. The capacity of empathy varies with personal development and it has its evolutionary significance. Studying the mechanisms and brain activities of empathy and its affecting factors really get a great importance and it is essential to human emotional behaviors. Results from recent neuroimaging and neurophysiological studies suggest that imagining or seeing the pain of others’ body or facial expressions may generate activation of the affective nodes and the sensorimotor nodes in pain matrix. Some fMRI researchers have indicated a relation between interpersonal relationship and empathy. And also, ERP components related to empathy has been found. According to ERP studies, in empathy, there was an early negative potential relating to emotion sharing and a late positive potential relating to social evaluation. So far, there were some studies focused on affecting factors on empathy. Our study mainly concerned the electrophysiology evidence of interpersonal relationship’s effect on empathy to test the meanings of empathy-related ERP components and the brain activation. Our event-related potential study recorded 14 right-handed subjects’ electrophysiology data by using priming paradigm in pain empathy task to investigate the influence of interpersonal relationship and its brain mechanism. The data of friend’s photo priming condition and stranger’s photo priming condition were recorded and compared with each other. Each condition contained two kinds of judgment, that is, pain judgment and no-pain judgment. We also used sLORETA to check out the brain activation of empathy and relationship’s effect on empathy. The study used IRI-C and combined its data to ERP amplitude data to verified neural mechanisms of empathy and the personal capacity by using correlation analysis. The study found that N1 amplitude was decreased in the friend priming condition of pain empathy decision task compared with N1 in the stranger priming condition, which indicated that N1 did have the effect of emotion sharing. Comparing with strangers, the similar neural network activated when people shard the emotion of their friends and made the N1 fall down. P3 amplitude was increased in the friend priming condition of pain empathy decision task compared with P3 in the stranger priming condition, which indicated that interpersonal relationship strengthen the conscious processing of cue perception and social cognitive evaluation in pain empathy. To investigate brain mechanisms of empathy we used software of sLORETA to complete the source analysis of N1 and P3 in the pain task under both two priming conditions. The results showed that pain judgments in both two conditions mainly activated the precentral gyrus, Brodmann 4and there was no significant difference between these two conditions. We found significant difference at 600-700 ms and 700-800 ms for P3 through Brodmann 22. And we also found positive relation between IRI-C and N1 and negative relation between IRI-C and P3. Interpersonal relationship did have effect on empathy either for pain. As showed in ERP results, for pain empathy N1 and P3 were regarded as automatic emotion sharing and controlled cognitive evaluation of pain. The study found that interpersonal relationship affected both the early automatic processing (N1) and the late controlled processing (P3) of empathy. N1 did have the effect of emotion sharing. Comparing with strangers, the similar neural network activated when people shard the emotion of their friends and made the N1 fall down. P3 shows that interpersonal relationship strengthened the conscious processing of cue perception and social cognitive evaluation in pain empathy.