Since the outbreak of COVID-19 in 2019, online-based learning has become a prevailing trend for studying subject matters globally. Additionally, there is an increasing number of international schools teaching CLIL courses to domestic students and many of them are conducting classes online during the pandemic in China. Although the Content and Language Integrated Learning (CLIL) approach has been widely researched in European countries [1], there hardly exists investigations of distance learning within the CLIL context in Asia, especially in China. Therefore, to fill the gap, this qualitative study investigates Chinese EFL students' differential perceptions, learning process, and learning challenges towards offline and online CLIL classes. Six participants (four females and two males), who are L2 learners of English of similar ages (from 17 to 19) studying the same curriculum from one international high school in China, participated in semi-structured interviews (each lasting for an hour) to retrospectively reflect upon their learning experiences in online and offline classes. The current study used the thematic approach to perform content analysis on the interview data, in terms of class course delivery, interaction, workload, and flexibility. The findings indicated that the online learning environment adopted more flexible schedules, which gave students more opportunities to search questions online immediately in class and self-initiated review after class. Nevertheless, students were more motivated in offline classes as they had more interactions with teachers and classmates and did not experience distractive technical issues in class. In addition to the new language challenges in online classes, lack of oral practice was the primary obstacle for students to improve their English proficiency and understand the content knowledge. The findings could provide CLIL educators with a deeper understanding of students' online learning attitudes and experiences so that they can better plan classes and prepare students to conquer potential learning challenges.