Since the 1990s corpora have revolutionized the study of language .Language pedagogy is one of the areas which have used corpora extensively . Leech observes a convergence between teaching and language corpora , which he thinks has three focuses ,namely the indirect use of corpora in teaching , the direct use of corpora in teaching , and further teaching-oriented corpus development . Presently corpora have primarily been used indirectly in language pedagogy while the direct use of corpora in teaching is largely confined to learners of more advanced levels . Nevertheless ,as long as the two tasks currently faced by corpus linguistics can be accomplished , corpora will play an even more essential rolein deciding what to teach and how to teach .Learner corpora as a kind of teaching-oriented corpus resources can be used either directly or indirectly in language pedagogy . A case study of passive constructions in the Chinese Learner English Corpus demonstrates that contrastive corpus linguistics provides a powerful tool for predicting , diagnosing ,and explaining learners'errors in their interlanguage in second language acquisition research .