Background: This study sought to analyze the structural relationships between optimism, distress tolerance, grief avoidance, intrusive rumination, deliberate rumination, and psychological well-being among undergraduates who have experienced a loss. Methods: Subjects comprised 435 university students (258 females and 177 males), with their duration of grief experience and the elapsed period from when the loss occurred having been taken into consideration. Results: Distress tolerance, grief avoidance, intrusive rumination, and deliberate rumination mediated the relationship between optimism and psychological well-being sequentially. Additionally, there were significant differences between the "less than 6 months" and "more than 6 months" groups in the structural relationships between optimism, distress tolerance, grief avoidance, intrusive rumination, deliberate rumination, and psychological well-being. Conclusions: The direct path of grief avoidance to psychological well-being was not significant, but it was found to have a significant effect through the sequential mediations of intrusive rumination and deliberate rumination. This result suggests the need for active intervention to allow people to face and cope with life after a loss, without avoiding the loss experience.