Abstract: Based on feedback theories, the paper examines the effects of three types of feedback (machine feedback, peer review and teacher feedback) on the revision of university students' English argumentative essays. 127 students from a prestigious university in Beijing answered the questionnaires, 47 of whom were interviewed. The results showed that the three types of feedback had their own merits and drawbacks and differed from one another in such aspects as focus, levels of being specific and serious, speed and interaction, that they all could identify the strengths and weaknesses in writing and offered suggestions accordingly, and that teacher feedback was the most effective, followed by peer review and machine feedback.