With the rapid growth of the Internet in China， the “information cocoon” has emerged in the Internet context of China， and has had an impact on the distribution and proliferation of mainstream ideology. The condition for “information cocoon”， from the perspective of its generation and development， is the “echo chamber effect”， that is， the repeated dissemination of homogenized information. When the audience is trapped in the homogenized information， it leads to the formation of the “information cocoon”， which may cause “group polarization”. The “information cocoon” may block the dissemination of mainstream ideology in the community， create conditions for the dissemination of wrong ideas and negative information in the group， and in extreme cases may even lead to fanatical online public opinion events. Thus， to reduce the negative effect of “information cocoon” on the dissemination of mainstream ideology， it is necessary to rouse netizens' civic awareness from the ideological level to eliminate the barriers of “information cocoon” as much as possible， carry out various ideological publicity for different types of “cocoon” from the cultural level， and build network supervision agencies from the legal level so as to ensure the timely supervision of information in emergency cases.