Abstract: Through a combination of experimental study and questionnaire, this study aims at exploring the effectiveness of flipped classroom. It compares students' CET-4 scores between the experimental class which adopts a flipped instruction approach and the controlled one which uses traditional lecture. The results indicate that learners are conservative about continuing to implement flipped classroom despite acceptance. The scores of the experimental group are not significantly higher than that in the controlled group. The study also attempts to analyze the causes and points out the potential problems in the process: time cannot be guaranteed due to the heavy load of coursework of engineering students; diversity learning activities lead to students' anxiousness; the flipped classroom poses challenges to the teacher; hardware facilities in local colleges and universities are urged to be strengthened. In a word, we need rational learning and thinking about the flipped classroom, realizing the optimal teaching effect in combination with the practical situation of students.