The aim of the study was to investigate the effect of online social support on secondary vocational students ′life satisfaction, and further explore the effect of belief in a just world as a cognitive factor and gratitude as a emotional factor between them. And a survey was conducted to examine the relationship among online social support, belief in a just world, gratitude and life satisfaction. The participants were 656 secondary vocational stu-dents; and four questionnaires were used in this study: Online social support questionnaire, belief in a just world scale, gratitude questionnaire and the satisfaction with life scale. The results indicated that: 1) the relationships between each pair of online social support, belief in a just world, gratitude as well as life satisfaction were sig-nificantly positive; online social support had no direct effect on life satisfaction, but could respectively predict be-lief in a just world and gratitude, which in turn significantly predict life satisfaction. 2) online social support af-fected secondary vocational students′ life satisfaction through two indirect paths: through the mediating role of be-lief in a just world; through the mediating role of gratitude.