Abstract: This paper presents the result of an experimental study by applying the self-writing-assessment to students' English compositions. The subjects divided into high-level and low-level groups are sophomores in a college in Yunnan.Before the experiment, both groups are trained how to assess their papers with the given self-grading standards. Then they are asked to finish an English composition on the same title and within the same phase of time in class. The results of students' self-assessment are then compared with those of the teachers by using ANOVA and Pearson correlation analysis. The results show that the high-level students' self-assessments and teachers' assessments are very close, while the low-level students can hardly make right judgments on their writing skills. In the paper the limitations of this study and future research directions are also pointed out.