Background <p>Against the backdrop of an increasingly ageing population, safeguarding the mental health and well-being of the older adults has become a shared societal consensus. This study focused on retired older adults and aimed to explore the impact of their retirement experiences on depression and life satisfaction, as well as the underlying mechanisms.</p> Methods <p>The Retirement Experience Scale, Social Participation Questionnaire, PHQ-9 Scale, and Life Satisfaction Scale were used to survey 296 retired older adults.</p> Results <p>Results showed that in the overall sample, positive retirement experiences significantly predicted life satisfaction through the mediating effect of social participation. Multi-group analyses revealed that among retired individuals who provided grandparental childcare, social participation significantly mediated the relationship between positive retirement experiences and depression, as well as the relationship between positive retirement experiences and life satisfaction. In contrast, social participation had no significant mediating effect among those who did not provide grandparental childcare.</p> Conclusions <p>These findings not only elucidate the mechanisms linking retirement experiences to mental health but also offer theoretical insights and practical implications for designing interventions within the active ageing framework.</p>