Objectives <p>First-year college students navigating the transition into emerging adulthood face heightened psychological vulnerability, particularly within competitive academic environments. This study examined whether a mindfulness-based intervention can&#xa0;enhance mindfulness and reduce psychological distress, and whether these effects operate through emotion regulation strategies, including cognitive reappraisal and expressive suppression.</p> Method <p>A cluster randomized controlled trial (cRCT) was conducted with 218 first-year students from a Double First-Class university in China. Participants in the intervention group completed an eight-session mindfulness-based program. Pretest and posttest data were analyzed using structural equation modeling within a residualized change framework, controlling for baseline measures and demographic covariates.</p> Results <p>The intervention significantly increased mindfulness over time relative to the control group. Posttest mindfulness was positively associated with cognitive reappraisal (<i>β</i> = 0.39, <i>p</i> &lt; 0.001) and negatively associated with expressive suppression (<i>β</i> =  − 0.26, <i>p</i> &lt; 0.001). Cognitive reappraisal predicted lower psychological distress (<i>β</i> =  − 0.22, <i>p</i> &lt; 0.001), whereas suppression predicted higher distress (<i>β </i>= 0.17, <i>p</i> = 0.012). Mindfulness also had a direct negative effect on distress (<i>β</i> =  − 0.22, <i>p</i> &lt; 0.001). Indirect effects through emotion regulation were significant (<i>β</i> =  − 0.13, <i>p</i> &lt; 0.001), accounting for 36.86% of the total effect.</p> Conclusions <p>Mindfulness reduces psychological distress through both direct and emotion regulation pathways. By focusing on first-year students in a hypercompetitive academic setting, this study demonstrates that early, mechanism-based mindfulness interventions can support adaptation and resilience during the transition into emerging adulthood.</p> Preregistration <p>This study is not preregistered.</p>