The susceptibility for posttraumatic stress symptoms (PTSS) appears to depend on individual personality traits and emotional regulation strategies. As a personality tendency to actively conceal from others personal information that is perceived as distressing, self-concealment can affect mental health through maladaptive emotion regulation processes. However, there is little research examining the links among self-concealment, maladaptive emotion regulation strategies, and PTSS. Alternatively, there is substantial empirical evidence supporting the effects of experiential avoidance and rumination on PTSS. Firefighters constituted a high-risk group for PTSS due to repeated exposure to traumatic events, but studies of PTSS have focused largely on the survivors of traumatic events while there is a paucity of research on firefighters. The object of this study was to investigate the effect of self-concealment on PTSS and the mediating effects of experiential avoidance and rumination in Chinese firefighters who experienced work-related trauma. This study included 215 male firefighters from 24 Fire?Alarm?squadrons in 3 large cities of Northern China (mean age ± standard deviation, 22.90 ± 3.38 years) who had experienced work-related trauma. Participants anonymously completed Chinese versions of the following self-report measures: Essen Trauma Inventory, Self-Concealment Scale, Nolen-Hoeksema Ruminative Responses Scale, Acceptance and Action Questionnaire-Second Edition, and Impact of Event Scale-Revised. Correlation analyses were performed using SPSS20.0. The path analysis model was tested using Mplus7.4. The Harman’s single factor was used to test whether there was a common method bias. The bias-corrected percentile bootstrap method was used to analyze multiple mediation effects. Correlation analysis revealed significant and positive correlations among self-concealment, experiential avoidance, rumination, and PTSS scale scores. Analysis of the structural equation model revealed that self-concealment can directly promote PTSS (total effect size = 0.427). There were two indirect paths from self-concealment to PTSS: the serial mediation by experiential avoidance and rumination, and mediation by rumination alone. The total indirect effect of self-concealment was 0.217, accounting for 50.82% of the total effect. In addition, 64 (29.77%) firefighters who had experienced work-related trauma exhibited severe PTSS as measured by the Impact of Event Scale-Revised. In conclusion, self-concealment affects PTSS both directly as well as indirectly by rumination and through the serial mediation of experiential avoidance and rumination. Thus, while self-concealment is often used by survivors as a self-protective strategy for emotion regulation, it may actually prove harmful in the long-term. These findings expand our understanding of how personality traits influence PTSS susceptibility and of the damaging effects of self-concealment on mental health. Effective prevention and treatment of PTSS must address the underlying contributions of self-concealment, experiential avoidance, and rumination. Further, this study found that firefighters are at high risk of PTSS. PTSS in firefighters warrants more intensive monitoring and research.