Flipped Classroom, as an emerging teaching mode, allows students to learn outside the classroom through e-learning and interact with the teacher in the classroom. It is widely used by many educational researchers both at home and abroad. Many studies on the Flipped Classroom are of teaching pattern and teachers' roles, but few are concerned about the changes of students' roles. Based on this situation, by doing questionnaire survey and student interview in Ningbo Dahongying University in Zhejiang Province, the paper discusses the changes of students' roles in Advanced English in terms of three class periods: before-class, in-class, and after-class. Students' roles have changed from passive learners in traditional classroom to be autonomous, confident, cooperative, and self-reflective learners in the Flipped Classroom. Also, existing problems of students' role transition are pointed out and relevant countermeasures are provided.