Background <p>Clinical internship is critical to nursing students’ professional development. Transition shock and imposter phenomenon are prevalent among interns and are linked to poor psychological adaptation.However, the moderating role of emotion regulation remains unclear.</p> Methods <p>A cross-sectional study was conducted among 384 Chinese nursing interns. Validated scales were used to assess transition shock, imposter phenomenon, cognitive reappraisal, and expressive suppression. Correlation and moderation analyses were performed.</p> Results <p>Transition shock and expressive suppression were positively associated with imposter phenomenon, while cognitive reappraisal was negatively associated with it. Cognitive reappraisal weakened the association between transition shock and imposter phenomenon, whereas expressive suppression strengthened it. No harmful multicollinearity was detected.</p> Conclusion <p>A positive association exists between transition shock and imposter phenomenon among nursing interns. Cognitive reappraisal and expressive suppression play opposing moderating roles. These findings enrich the stress-coping model and support emotion regulation interventions in nursing education. Causal inferences cannot be drawn due to the cross-sectional design.</p> Clinical trial number <p>Not applicable.</p>