Social network sites (SNSs) have integrated into people’s daily life. The impacts of social network site use have received much attention from relevant scholars. Previous studies mainly focused on active use of social network site such as self-presentation or self-disclosure. They found that self-presentation and self-disclosure contribute to increases in social capital, self-esteem and life satisfaction, as well as decreases in loneliness. However, social network site also makes it easier for individuals to obtain others’ information. Many people passively use social network site for content consumption without disclosing information. Studies revealed that passive use of social network site had negative effect on emotional well-being and life satisfaction which are two key factors of subjective well-being. However, less is known about the underlying mechanism that passive use of social network site influences subjective well-being. According to social comparison theory and existing studies, upward social comparison may be a vital factor playing mediating roles in the association between passive use of social network site and subjective well-being. In addition to the mediating effect of upward social comparison in passive use of social network site and subjective well-being, there might exist chain mediation of upward social comparison and affects in the association between passive use of social network site and life satisfaction. To investigate the relationships among passive use of social network site, upward social comparison, passive affect, negative affect and life satisfaction, a survey research method was conducted in which scales for passive use of social network site, upward social comparison, positive and negative affect as well as life satisfaction were administered to 1168 undergraduate students. Data were collected and analyzed with SPSS 17.0 and Amos 20.0. The results indicated: (1) Passive use of social network site was positively associated with upward social comparison and negative affect, and negatively associated with positive affect and life satisfaction; upward social comparison on social network site was positively related to negative affect and negatively related to positive affect and life satisfaction; positive affect was positively related to life satisfaction and negative affect was negatively related to life satisfaction. (2) Passive use of social network site had no significant direct effect on positive affect, negative affect and life satisfaction, but it could predict them through the mediating effects of upward social comparison. (3) Passive use of social network site could also predict life satisfaction through two chain mediating effects: through the chain mediating role of upward social comparison and positive affect; through the chain mediating role of upward social comparison and negative affect. These findings highlights the mediation of upward social comparison in the association between passive use of social network site and subjective well-being, as well as the chain mediating effects of upward social comparison and affects. They may contribute to a better understanding of what the effect of passive use of social network site on subjective well-being is and how passive use of social network site influences subjective well-being. Besides, the present study can offer some useful suggestions for protecting and promoting subjective well-being in the Internet age.