Focusing on the emotion expression of college students when they use social media，the study try to use questionnaire method and in-depth interview to find out the characteristics and motivations of the emotional expression in social media. The survey finds that college students’ emotional expression in cyberspace is more abundant than in real life；not only the use of multiple social media to express different emotions，but also the use of text，pictures，facial expressions and other symbols to express emotions；although the content of emotion expression is more complex，but the main of that is expression of positive emotion；the main motivations of emotion expression are interactive sharing，social support and self-encouragement，and are closely related to interpersonal communication through network. At the same time，the study also find that the expression of the emotion of college students on social media has some problems：such as show，excessive impression management，the lack of immediate expression tools and so on.