Covid 19 virus broke out in Vietnam in recent days. Schools in the provinces have dropped students out of school and let students study online. Although this helps us to prevent disease effectively. But it also has negative effects. Firstly, the knowledge we learn in school is very detailed and complete. But when I returned to study online, the amount of knowledge narrowed a lot. We will not understand the lessons when studying online than when studying in class. Second, when studying in class the teacher can control his own students. But when studying online, teachers cannot control them, so it is easy for students to skip class, or work separately while studying. Third, some students who study online will not be able to acquire the same knowledge as they do in class, so they will learn more slowly than other students. To overcome this situation, I have the following specific actions: Firstly, we can both study in class with practice exercises. Wherever we do not understand, we can ask our friends, who learn better than us. Thereby, we can learn the lesson better. Next, teachers choose teaching methods that are interesting to students and inspire students to enjoy learning. Teachers should also coordinate with parents to supervise students' learning, creating effectiveness for teaching. And finally, the most important thing is our consciousness, let's give ourselves a sense for online learning, to avoid narrowing knowledge. Let's learn because we cannot know those online learning, which can help us a lot