Since 2005, Dana Technology has started to use the O2O teaching mode: teachers give lectures in one classroom and spread them to different classrooms through synchronous video, which breaks through the limitation of hardware such as classroom size. Therefore, although Dana Technology has become the first in the industry, there are only 79 lecturers. In order to ensure the learning effect, Dana insists on the way of simultaneous lectures and live broadcasts, and never records. "We found that as long as the recorded videos can't interact, students' enthusiasm for learning will drop immediately. "An executive of Dana Technology said that in order to ensure the learning effect, Dana Technology recruited a large number of teaching assistants, and each line had 1-2 people after work. While ensuring classroom discipline, answer all kinds of questions that the teacher has not answered remotely. In Dana's teaching scene, although the lecturer is not on the scene, the teaching assistants pass by the students at any time to guide them to deal with various problems.