The outbreak of COVID-19 at the beginning of 2020 has formulated a totally different teaching situation for most of Chinese Universities/Colleges, because inevitably online courses took the leading role in teaching by replacing in-class courses at the beginning of that semester, then in a parallel teaching mode after students' returning to school. This research conducted a comparative study on teaching quality of online courses and in-class courses under this specific background from Chinese college students' perspective by using in-depth interviews and the online questionnaire. This study finds that the quality of online courses is not as good as in-class courses at present, but with a small gap to improve, indicating a positive affirmation and encouragement of improvement for online courses. Furthermore, teaching paradigms have significant impacts on imparting knowledge. Teaching paradigm is the "catalyst" and "accelerator" on the basis of the teachers' own professional knowledge, which facilitating both teaching and learning. Finally, different learning atmosphere (online courses / in-class courses) is a significant factor in explanation of different effects and influences on both teachers and students. A more advanced network technology is needed to create a more interactive and communicative "learning atmosphere" of online courses, thus gradually improving the effect of online courses.