TEM4 (Test for English Majors-Band 4) is one of the important English proficiency tests for college English majors in China. It links and evaluates the status quo of the teaching and learning process, provides feedback and guide for teachers and students. The impact of testing on teaching is called the backwash effect, which includes both positive and negative aspects. This paper analyzes the positive and negative backwash effects TEM4 brings to the teaching and learning of Comprehensive English, one of the core courses for English majors, and discusses how to exert its positive effect and reduce the negative effect to promote teaching effectiveness, help students improve their language knowledge and skills to prepare for more effective examinations.