The guidance effect of teacher feedback in contemporary English writing has been a hot topic for research. More and more researches focus on the effect of teacher feedback in senior high schools or universities. This research analyzed the supervisor feedback on 32 undergraduate thesis revisions from 8 students from three aspects: error feedback, non-error feedback and the focus of supervisor feedback. The results show that both error feedback and non-error feedback can significantly improve the overall expression of papers; while their focuses are quite distinctive. Suggestions on how to optimize teacher feedback are put forward.