Abstract: Under the theoretical framework of output-oriented approach, this paper takes an intelligent marking platform as an example to investigate the teacher-assisted feedback mechanism in college English writing teaching. It is found that the teaching of college English writing based on intelligent marking is limited by the intelligent level of the system, and problems such as poor recognition of long sentences and misjudgment of grammar are frequent, which need to be compensated by teachers' feedback. Teacher assistance should be aimed at the problem of insufficient intelligence degree, combining online and offline to establish a diversified feedback mechanism; the teacher-assisted feedback can improve students' writing enthusiasm and individual and overall writing ability. The complexity of writing task has an impact on the improvement of students' language ability.