To investigate the relationship between disaster exposure and posttraumatic growth, as well as the mediating role of cognitive emotion regulation and the moderating role of dark personality traits, a study was conducted among 1,508 individuals who experienced severe flooding in Henan Province on 20 July 2021. The participants completed measures including the Disaster Exposure Scale, the Posttraumatic Growth Scale, the Cognitive Emotion Regulation Scale and the Dark Triad Scale. Results showed that (1) disaster exposure had a significant negative predictive effect on posttraumatic growth; (2) adaptive cognitive emotion regulation and maladaptive cognitive emotion regulation fully mediated the relationship between disaster exposure and posttraumatic growth; (3) the front path, direct path, and back path of the mediating effect of dark personality traits were involved in the relationship between maladaptive cognitive emotion regulation and posttraumatic growth. The practical implications of this study suggest that targeted assistance can be provided through psychological interventions and self-management training to enhance posttraumatic growth, alleviate the negative impact of disaster exposure, and promote psychosocial well-being.