While more Chinese students are going abroad to persue their further academic study, how to help them improve academic writing competence has received wide attention. Modality, as one of the complex areas of English grammar, reflects the writer's attitude and is extremely important in academic written discourse. Therefore, it is necessary to investigate how Chinese learners of English use modal verbs. For this purpose, a learner corpus (LC) with Chinese learners' academic writing has been compiled and compared against a professional corpus (PC) which consists of published research articles. With the help of software Antconc 3.2.4w, the use of nine core modal verbs in both corpora has been explored. Findings indicate that compared with professional writers, Chinese learners tend to use modal verbs more frequently; they also tend to overuse can, will, could and would and underuse may. Based on an analysis of the two corpora, this study proposes possible reasons that account for these differences. This study provides some insights into the use of modal verbs by Chinese learners of English and thus informs teaching of modal verbs in the English classroom and contributes to the academic writing curricula design.