In flipped classrooms, the preparatory work for college teaching is to record videos and design thinking questions before class. Video is one of the important components. Teachers convert the process of explanation into video, and students watch the video for pre-class learning. In this video, the requirements of teachers are put forward, one is to ensure the correctness of the teaching of knowledge points, and the other is to make a scientific and reasonable explanation for the situation of students. Teachers also need to design a certain number of questions for students to think about during the pre-class study, and students can also discuss each other to improve students' mastery of pre-class knowledge.