Background <p>Improving the mental health and digital divide issues is crucial for promoting active aging. This study aimed to examine the bidirectional relationship and intricate mechanisms between social participation, social media use, and depressive symptoms among a nationwide sample of Chinese older adults.</p> Methods <p>We utilized data from two waves (2018, 2020) of the China Health and Retirement Longitudinal Survey, which included 4928 older adults aged 60 years and above. We Used a cross-lagged model to examine the bidirectional relationship between social participation, social media use, and depressive symptoms.</p> Results <p>In two years, social media use competency and social participation frequency can be predicted bidirectionally, and social media use competency and depressive symptoms can also be predicted bidirectionally. However, there is no cross-temporal bidirectional relationship between social participation frequency and depressive symptoms. Depressive symptoms can predict social participation frequency two years later, while social participation frequency cannot directly predict depressive symptoms. The mediation analysis indicated that social media use competency played a complete mediating role between social participation frequency and depressive symptoms.</p> Conclusions <p>Continuous social participation may enhance social media use competency and alleviate depressive symptoms in older adults. Social media use may alleviate the decrease in social participation frequency and increase in depressive symptoms in older adults. Therefore, social media can be an effective tool to promote the integration of the older adults into society and alleviate negative emotions.</p>