Introduction: Older adults are prone to high levels of depression due to their deteriorating physical functions and shrinking social networks after retirement. Volunteering as an important social activity is essential for alleviating depression by building social network. This paper aims to examine the effect of volunteering on depression among older adults by using China Longitudinal Aging Social Survey (CLASS 2018) data. Methods: This study uses descriptive analysis and chi-square tests to show differences in demographic factors of older adults' volunteerism participation, followed by bivariate correlation analysis to examine the correlation between the vital variables. Afterward, stratified linear regression analysis is used to research the significant level and impact between volunteering and degree of expertise, frequency, and variety of participation. Results: 8,459 older adults are included in study. The research reveals that older adults who are younger, live in urban areas, are married, or have a higher degree of education tend to have fewer depressive symptoms. Meanwhile, participation in volunteering (OR = 0.90, 95% CI: 0.8, 1.1, p < 0.001), as well as that demands specialized skills (OR = 0.51, 95% CI: 0.30, 0.2, p < 0.001), more frequency of participation (OR = 1.85, 95% CI: 1.53, 2.18, p < 0.001), and a wider variety of activities (OR = 0.21, 95% CI: 0.12, 0.29, p < 0.001), all have a positive influence on depression levels. Discussion/ Conclusion: Older adults who participate in voluntary services have lower depression symptoms and should be encouraged to use their professional skills and increase participation frequency and variety in this process. This article suggests that governments should help older adults participate in voluntary services by time bank which will further strengthen social ties, rebuild social networks and alleviate depression symptoms of older adults.