University students, particularly those with experiences of being left behind, face difficulties dealing with the many changes that cause psychological problems, and meaning in life plays a protective role in this process. Mindfulness and social support have emerged as potential factors influencing meaning in life. Although previous studies have revealed a link between mindfulness and meaning in life, few studies have examined this relationship from the perspective of the experience of being left behind. A sample comprising 1205 university students was used for the study. Self-report questionnaires were administered to assess the degrees of mindfulness, social support, meaning in life, and the experience of being left behind. We established four moderated mediation models to test the moderation and mediation effects. The results of a moderated mediation analysis revealed that social support and its dimensions mediated the effect of mindfulness on meaning in life. The impact of family support on meaning in life was moderated by the experience of being left behind, and friend support and other types of support had no significant moderating effects. Specifically, the moderating effect of the experience of being left behind significantly attenuated the impact of family support on meaning in life, whereas no significant weakening effect was observed for friend support or other types of support. Therefore, psychological education should emphasize the compensation role of friend support and other social connections in the psychological problems caused by the experience of being left behind, and appropriate mindfulness intervention is suggested.