Abstract: When the various individual feelings converge into a collective emotional expression, the social mood appears. The expression of social mood is difficult in traditional media circle for the strict examination and regulation. The internet constitutes to be a positive platform for social operation when emotional expression is much more easily realized here.  Nevertheless, the negative effect cannot be neglected. Here comes a new social topic, the social emotional expression in social psychology discipline. We should emphasize on the importance of this problem for it is a key point in the function realization in web communication and a crucial factor in social stability and harmony.

Key words: Web, Web Communication, Social Mood, Society