Based on the data of 2018 CHARLS, the study use linear regression model, stepwise regression and product of coefficients approach to analyze the influence of volunteer participation on life satisfaction and the mediating role of depression. Moreover, the age-group differences in the mechanism are further explored. The findings revealed that volunteer participation was both directly and indirectly associated with life satisfaction among middle-aged and older people (β=0.041，P<0.05). Depression was found to mediate the relationship of volunteer participation to life satisfaction, and the mediating effect accounted for 22.75%. Furthermore, the influence coefficient and mechanism of volunteer participation on different age groups are obviously different. The results have important value for preventing and intervening depression, improving the mental health and life satisfaction among middle-aged and older people, and promoting active aging.