Relative deprivation is a kind of subjective psychological feeling, which affects individuals' cognition and emotions through unreasonable social comparison, and makes individuals make aggressive behaviors that harm others. As a special social group, the closed environment of prisoners leads them to a weak position in social comparison, which is easy to have a sense of relative deprivation and lead to strong aggression. This paper uses 416 prison inmates to investigate the mechanism of relative deprivation on aggression, and the mediation and regulating role of hostile attribution bias and social support. The study found that prisoners have a strong sense of relative deprivation, which significantly positively affects aggression, and hostile attribution bias plays a partial intermediary role, and is regulated by understanding social support.