This study investigates the different effects of teacher feedback,peer feedback and online feedback on college students' writing skills.The results indicate that(1) teacher feedback has a significant role in enhancing students' awareness of writing structure;(2) peer feedback and online feedback are effective in improving students' writing content and language,reducing their writing anxiety,and developing their writing interest;(3) most students prefer that the teacher adopts flexibly different types of feedback so as to ensure the positive effects of each type of feedback.