Objective To explore the positive mental character dimmensions affecting the well-being of junior high school students. Methods In the first week of the new semester during the winter vacation on February 17， 2024， cluster sampling was used to select 405 junior grade one students from a school in Beijing for the study. Engagement， Perseverance， Optimism， Connectedness and Happiness （EPOCH） measure and Middle School Students' Positive Psychological Quality Scale were used to investigate the students' well-being and positive mental characters. Patient Health Questionnaire-9 （PHQ-9） and Generalized Anxiety Disorder-7 （GAD-7） were used to measure mental health. Self-rating Internet Gaming Disorder Scale （IGDS） and Chinese Family Assessment Instrument （CFAI） were used to assess the risk of internet gaming disorder and their family function. The mechanisms of action between positive mental characters， depressive disorder and well-being were analyzed by mediating effects. Pearson correlation and stepwise multiple regression were used to explore positive mental character dimensions that predicted well-being. Results A total of 405 junior grade one students had a total score of （71.35±16.44） on the EPOCH measure. Positive mental characters score and family functions score of junior grade one students were positively correlated with well-being score （r=0.689， 0.591； all P＜0.05）， depressive disorder， anxiety and internet gaming disorder scores were negatively correlated with well-being （r= -0.586，-0.516，-0.320； all P＜ 0.05）. Positive mental characters partially mediated the relationship between depressive disorder and well-being， with an effect value of -0.147， which accounted for 25% of the total effect. Transcendence and altruistic strengths mediated the most significant effect on well-being （P ＜ 0.001）. Conclusions Positive mental characters are highly correlated with junior high school students' well-being， with the dimensions of transcendence and altruistic strengths being the strong predictors of well-being.