<p>This study aimed to investigate how and when SNS addiction affects executive functions (EFs). Specifically, we examined (1) the mediating effect of three psychological traits (self-control, stress, and anxiety) and (2) the moderating effect of three engagement conditions (normal, stressful, and distracting). The SNS addiction levels and psychological traits of 251 participants were self-reported. The executive function of the participants, including inhibition, working memory, and switching, was assessed with computerized stop signal, Corsi block tapping, and category switch tasks, respectively. Results indicated that SNS addiction was positively associated with anxiety and stress and negatively with self-control. Under a normal test condition, anxiety and stress were positively associated with inhibition. In the stressful engagement condition, SNS addiction was positively associated with inhibition. Moreover, anxiety was negatively associated with working memory and stress was positively associated with switching, while self-control was negatively associated with inhibition but positively associated with working memory. In the distracting engagement condition, SNS addiction was negatively associated with working memory. Furthermore, both anxiety and stress were negatively associated with switching, and self-control was negatively associated with working memory. This study extends the literature on the manifestations of SNS addiction, focusing on EFs under different test conditions.</p>