<p>Final exams represent a typical stressor for university students. This study examines the impact and underlying mechanism of excessive short-video apps use on students’ test anxiety during the final exam period. Using a 10-day diary design, data were collected from 190 Chinese university students to examine the dynamic relationship between short video usage and test anxiety, with mindfulness included as a mediating variable. Multilevel structural equation modeling was employed to differentiate effects at both the within-person and between-person levels. The results showed that excessive use of short-video apps significantly and positively predicted test anxiety at both levels. Moreover, mindfulness partially mediated this relationship. Further analysis revealed that the mediation pathway differed by gender, reaching significance only among female participants. These findings support the Conservation of Resources (COR) theory by illustrating how excessive use of short-video apps may deplete psychological resources such as mindfulness, thereby exacerbating test anxiety. This study underscores the protective role of mindfulness in high-pressure academic contexts and offers theoretical and practical insights into the psychological consequences of emerging media use among students.</p>