Objective: To explore the relationship between aggression and category perception of angry expression in reform school students under social exclusion, so as to provide reference for the reform school students mental health promotion. Methods: In May 2023, 144 students were randomly selected from a reform school in Guizhou Province, and were divided into high and low aggression groups(77 and 67 students) by Aggression Questionnaire. Cyberball game was used to induce social exclusion and acceptance, subjects were divided into high aggressive exclusion group ( n =42), high aggressive acceptance group ( n =35), low aggressive exclusion group ( n =37) and low aggressive acceptance group ( n =30). All the participants completed the discrimination and identification tasks of category perception paradigm, and the relationship between aggression and category perception of angry expression of reform school students under social exclusion was analyzed by using category turning point, identification curve and analysis of variance. Results: The total score of aggression(97.34±8.00) and four dimensions (physical aggression: 29.75± 4.61, verbal aggression:17.19±2.58, anger:22.29±3.66, hostility:28.10±3.54) in the high aggression group were higher than those in the low aggression group(74.10±9.02，21.09±4.98，14.30±2.66，17.16±3.83，21.55±3.88), and the differences were statistically significant ( t =16.38, 10.85, 6.62, 8.20, 10.59, P <0.01). For identifying the turning point of the fear anger continuum, the social exclusion group（2.58±0.07）was significantly smaller than the social acceptance group（2.79±0.07）( F =4.85, η 2=0.07, P < 0.05 ）, and the social exclusion group had a tendency to shift the category boundary to the fear side. For identifying the slope at the angry happiness continuum category boundary curve, the high aggression group (0.63±0.03) was significantly higher than the low aggression group (0.53±0.03)( F =5.38, η 2=0.08, P <0.05). In the fear anger continuum,the high aggression group[(694.86± 78.29 )ms] reacted more quickly than the low aggression group[(660.70±79.86)ms]( F =5.08, η 2=0.05， P <0.05) In the angry happiness continuum, there was no statistical significance of social exclusion and aggression( P >0.05). Conclusions The suggests that social exclusion can lead to hostility attribution bias in individuals, while aggression can make individuals more sensitive to angry expression. The mechanisms by which social exclusion and aggression affect expression category perception are independent rather than interactive. The society should give tolerance and acceptance to reform school students, reduce exclusion and discrimination, and the reform education department should correct the aggressive behavior of reform school students and promote their mental health.