As the COVID-19 epidemic spreads across the globe, home-based online class has become the mainstream learning form of university students. With the development of the Internet era, online learning has become increasingly popular among university students. However, it seems that the effect and the quality of online learning caused by the change of teaching mode (i.e., the original offline traditional teaching is changed into online teaching) is not satisfactory and students’ learning engagement is also not ideal. Indeed, students’ learning engagement situation determines the quality of learning. The difference caused by the change of teaching contents and teaching forms of online learning significantly influences the learning engagement of students. Therefore, for the current online education, it is urgent to improve students’ learning engagement under the network learning environment (i.e. improving students’ time and energy invested in learning activities), which will be of great significance to the normalization and sustainable development of online learning. Based on the brand-new educational transformation environment, this paper constructs a research model of students’ learning engagement in order to explore the factors that affect students’ learning engagement. To be specific, this paper conducts a questionnaire survey on the Chinese university students who take online course (including Chinese Overseas students), uses SPSS22.0 and AMOS24.0 statistical analysis tools to analyze the survey data, and explores the impact of teachers, students and environmental factors on students’ learning engagement respectively. The factors of teacher include four aspects: teachers’ support, the relationship between teachers and students, interactive communication and knowledge teaching. The factors of students also include four aspects: the students’ independent learning ability, learning motivation, learning style, and engagement perception of teachers. The factors of learning environment refer to the external environment that promotes students’ knowledge construction and improves students’ learning engagement. As shown by the results, teacher factors, student factors and the environment factors are positively correlated with the learning engagement to a different degree. There are two different online teaching methods, recorded lectures and live lectures. In particular, teacher factors have different degrees of influence on students' learning engagement. The research results of this paper will have an important reference value to the research of effectiveness of online teaching for university students in the current and Post-Corona Era