Abstract: The effect of WeChat public opinion on group events has become increasingly obvious， and its superposition effect has changed the transmission structure of public opinion， bringing great public opinion governance challenges to the administers. Based on an analysis of the environmental group events in A City， it was found that the group events of the WeChat platform are characterized by the superposition of communicators， the superimposition of dissemination channels and the superposition of dissemination contents. Under the influence of the multi-superposition of WeChat， the mass mobilization forces of group events tend to ferment rapidly and the outbreak process may be accelerated catalytically while the event continues to evolve and upgrade which easily leads to secondary events. The government should establish the risk prevention and control awareness of WeChat superposition effect， strengthen the legislative supervision and protection， and reinforce the blocking management of WeChat superposition effect so as to avoid the evolution and upgrading of events.

Key words: WeChat, public opinion, superposition effect, environmental group event