Practice and research in the composition education that is using computer and network have been more and more active. Through online composition system, a large amount of written texts produced by students and teachers can be collected. This kind of information is called a learner corpus, which is important in second language education because the specific learning situations of learners can be analyzed. However, there is still little effective application on how to utilize the collected learner corpus in pedagogy. In this research, a web based composition/correction system has been constructed. It can not only support online composition submission and correction, but also supply a retrieval function for learner corpus. This function has been combined with another CALL (Computer Assisted Language Learning) drill system to create more effective exercises according to learners' misuses. This research has proposed a unique mechanism to integrate both construction and application of learner corpus.