Along with the development of science and technology and the popularization of network, social networking sites (SNSs) have become an important platform for interpersonal interactions, and the impact of SNSs use has also become a focus of relevant research scholars. Teenagers are the most active users in SNSs, so it’s important to find out the impact of SNSs use on teenagers’ physical and mental health. Plenty of researches have investigated the relationships between SNSs use and teenagers’ psychosocial functioning. On the other hand, a great deal of researches interested in body image satisfaction. The past researches confirmed that media use impacts body image satisfaction from many perspectives. The current research focuses on the impact of SNSs use on teenagers’ body image satisfaction. The purposes of this research are to investigate the mechanism of SNSs use affecting body image satisfaction. A survey was conducted to evaluate relationships among SNSs use, body image comparison, body image satisfaction, and self-objectification of middle and high school students. Participants of the research were 1469 middle and high school students, including 733 girls and 736 boys. The experiments conducted questionnaires to the selected classes by convenient sampling. Four questionnaires were used in this study. the Scale for Social Networking Sites Use Intensity includes 8 items in which the first two measure Length of time on SNSs per day and online friends numbers and the other six using a 5-point Likert scoring. The SNS Appearance Comparison Scale includes 3 items using a 5-point Likert scoring and the Body Image States Scale includes 6 items using a 9-point Likert scoring. The Self-objectification Scale includes 10 items needed to be ranked in influential order. The results indicated that: (1) the SNSs use intensity of teenagers positively correlates with body image comparison on SNSs, and negatively correlate with body image satisfaction; and girls’ (not boys’) body image comparison negatively correlate with body image satisfaction. (2) For female teenagers, SNSs use not only directly predicts body image satisfaction, but also indirectly predicts body image satisfaction through the mediating role of body image comparison; and higher self-objectification predicts more body image comparison and less body image satisfaction. Those findings supported conclusion from earlier studies, that is, body image comparison is the reason for SNSs use predicting body image satisfaction. In addition to this, the research proved that self-objectification is the moderating role. Substantial research confirmed that body image affects multiple aspects of psychosocial functioning. It is why the research about teenagers’ body image is necessary. The findings of this research point to some practical implications. Firstly, teenagers (especially girls) should be guided to use social networking sites properly. Further education of media use such as media literacy involved in social networking sites might prove more effective. Then it is important to cultivate girls’ positive body image and reduce mass media objectification of female image. Social culture should encourage girls to enhance competence rather than pay attention to appearance. The negative effects of body image comparison could be reduced if girls don’t drive for and internalize the media ideal image.