This article explores the relationship between the metadiscourse and writing quality through examining the use of metadiscourse devices with longitudinal design and textual analysis.The findings reveal that metadiscourse is an effective way to improve writing level.In general,textual metadiscourse correlates positively and significantly with writing quality,while interpersonal metadiscourse does not.For the subtypes of metadiscourse,the significances only exist in logical,topical and additive connectives.And the use of connectives is simplistic with misusage.So the key to teaching lies in guiding students to know how to use metadiscourse devices appropriately and variably.