Today the new teaching theories and models are emerging frequently, both teachers and students, as the decisive factors in teaching, their roles are changing. In the college English class, the traditional role of teachers is being challenged. This study analyzes the historical development of PBL and its connotation, and pointed out that under the new concept, the new model background, teachers and students should reposition their roles in teaching. They should constantly update their concepts, to improve their literacy, to adapt the current education reform.