Developmental assessment,process-oriented and student-centered,aims at students' performance in learning process,and their development.The author of the paper conducted an empirical research of developmental assessment to her own students.By comparing the students' learning attitude,interest,motivation,strategies,performance and achievements in the experimentalclass with those in the controlled one,she found that developmental assessment had developed the students' comprehensive lan-guage competence,increased their grades in written examinations,especially in the final examination,and recorded their progressover time to have them a sense of accomplishment and become more self-confident,active,responsible and independent.There-fore,developmental assessment is an effective and reasonable assessment in the current polytechnic English teaching.