<p>Military recruits undergo a transition from local youth to qualified soldiers, which subjects them to pressure. Previous research has focused on the relationship between perceived stress and cognitive flexibility; however, researchers have largely overlooked the mediating processes underlying this association, particularly among military recruits. This study aimed to identify the mediating roles played by emotional resilience and posttraumatic growth (PTG) in this relationship. A convenience sampling method was used to select 8509 military recruits from western China. The survey administered to these recruits included a general demographic information questionnaire, the Chinese version of the Perceived Stress Scale (PSS), the Cognitive Flexibility Inventory (CFI), the Emotional Resilience Scale (ERS), and the Post-Traumatic Growth Inventory (PTGI). A mediation analysis was conducted to examine the potential process through which emotional resilience and PTG mediate the relationship between perceived stress and cognitive flexibility. (1) The findings reveal significant correlations among perceived stress, emotional resilience, PTG, and cognitive flexibility. (2) Perceived stress is negatively correlated with cognitive flexibility (<i>β</i> = -0.32, <i>P</i> &lt; 0.001). Emotional resilience and PTG not only mediate this relationship but also play chain mediating roles in shaping the relationship between perceived stress and cognitive flexibility. Perceived stress is observed to be significantly related to the cognitive flexibility of military recruits. This relationship is mediated by emotional resilience and PTG—both independently and sequentially—on the basis of a chain mediation model. These findings explain the patterns underlying these associations and provide a theoretical reference for interventions aimed at improving cognitive flexibility.</p>