Objective: To explore the relationship among dark triad, peer relationship, and cyber bullying of middle school students, and to provide suggestions for intervention of cyberbullying behavior of middle school students. Methods: Peer Relationship Scale (PRS), Dirty Dozen (DD) and Cyberbullying Questionnaire (CBQ) were administrated to 1 934 middle school students in Beijing and Yunnan by cluster sampling. Results: Middle school boys scored significantly higher on the dark triad and cyber-bullying than girls ( F =13.45, 50.20, P <0.01). The dark triad of middle school students was positively correlated with cyber-bullying ( r =0.38, 0.40, 0.21, P <0.01), while negative dimensions of peer relationship were positively correlated with cyber-bullying ( r = -0.10 , -0.22, -0.16, P <0.01). Peer relationship had a moderating effect on the relationship between dark triad and cyber-bullying ( β =-0.07， t =-3.24，Δ R 2=0.00， P <0.01). Conclusion Positive peer relationship can reduce the cyber-bullying behavior of middle school students with high dark triad which should be emphasized among middle school students.