Online education is a hot topic that is widely concerned in various countries today. In the era of mobile internet, countries around the world have made various effective attempts at online education, but online education is more of a supplement to school education, and large-scale normal online education lacks cases. The "School's Out, But Class's On" campaign launched by the Chinese government during the COVID-19 epidemic created a large-scale, normal online education application. We analyzed the background of this large-scale online education, clarify the foundation of large-scale online education, and reveal the impact of the largest online education activities on society and education.