Integrating cognitive appraisal theory of stress and attachment theory, the current study explored the influence of daily workplace ostracism on employee short‐term work engagement and examined the mediating role of negative work reflection and the moderating effects of employee attachment styles (i.e., attachment avoidance and attachment anxiety). To test the theoretical model, we employed an experience sampling method to collect daily diary data over 10 consecutive workdays, resulting in a final sample of 834 observations drawn from 133 participants. Results of multilevel path analysis indicated that daily workplace ostracism was negatively related to employee next‐day work engagement through negative work reflection at night. In addition, we found that employee attachment avoidance not only moderated the within‐person relationship between daily workplace ostracism and negative work reflection at night but also alleviated the indirect effect of daily workplace ostracism on next‐day work engagement via negative work reflection at night. Taken together, our study contributed by unfolding the dynamic cognitive appraisal process of workplace ostracism and identifying the significant role of attachment avoidance in shaping employees' cognitive reactions to daily workplace ostracism.