Self-disclosure is defined as the revealing of personal information to another person. With the development of modern communication technology, self-disclosure has gradually spread to online communications, especially in the platform of social networking sites (SNS). In SNS, self- disclosure could be displayed in various ways, such as posting or updating status, uploading photos, issuing a log and making comments. As a ubiquitous behavior in the use of SNS, self- disclosure on SNS is now in the focus of relevant research with its impact on adolescents’ psychological and social adaptation. In addition, with the rise of positive psychology, life satisfaction, a key component in well-being, gradually becomes a typical indicator of psychological and social adaptations. Therefore, this study attempted to explore the relationship between self-disclosure on SNS and adolescents’ life satisfaction, as well as the potential mechanisms underlying this relation. From the perspective of positive psychology, self-disclosure contributes to better physical and mental health (e.g., life satisfaction). Some empirical studies have also indicated that self-disclosure on SNS has a significantly positive effect on life satisfaction, and friendship quality might play an important role in this relation. In adolescence, peer relationships (e.g., friendship quality) play an increasingly important role in adolescents’ development and adaption, resulting from the transformation of relative importance of parents-adolescents relationships and peel relationships. Meanwhile, adolescents’ friendship quality is also influenced by their self-disclosure on SNS. As a result of a relatively high degree of overlapping between SNS friends and offline friends, adolescents could tell their friends about their current situation and status via SNS according to Connecting Developmental Constructions and Enhancement Hypothesis. To sum up, self-disclosure on SNS can predict adolescents’ life satisfaction through friendship quality. What’s more, the amount of relationship between self-disclosure on SNS and friendship quality depends on the expansively social tendency, according to the conditionality of Enhancement Hypothesis. Expansively social tendency is a newly-created variable, referring to the degree of how much SNS was used to communicate with offline friends. To conclude, the present study constructed a moderated mediation model exploring the relationship among self-disclosure on SNS, friendship quality, expansively social tendency and life satisfaction. A sample of 1556 students from 4 middle schools was recruited in the study to complete the self-report questionnaires. Four questionnaires were used in the study: questionnaire of self-disclosure on SNS, SNS use, friendship quality and life satisfaction. The results indicated that: (1) Self-disclosure on SNS was positively correlated with adolescents’ quality friendship and life satisfaction, while all of them were not correlated with expansive social tendency; (2) Friendship quality partially mediated the effect of self-disclosure on SNS on adolescents’ life satisfaction. Self-disclosure not only directly influenced life satisfaction of adolescents, but also, through influencing friendship quality, ultimately influenced adolescents’ life satisfaction. (3) Expansively social tendency moderated the mediation effect of quality of friendship on the relationship between self-disclosure on SNS and life satisfaction. This mediation effect was only found in individuals with high expansively social tendency, but not in less those with low expansively social tendency. The study revealed the complex mechanism between self-disclosure on SNS and adolescents’ life satisfaction. Self-disclosure on SNS influenced adolescents’ life satisfaction through friendship quality, and the mediation effect of friendship quality was influenced by expansively social tendency.