This present research was designed to explore how and to what extent explicit knowledge of L2 chunks and chunking, which have both grammatical and idiomatic information, would benefit English learning and use. The operation of an EFL learner's explicit L2 chunks and chunking knowledge has been qualitatively investigated over a 6-month period.Through ethnographic data collecting methods such as observations andinterviews of the participant's process of acquiring L2 knowledge system, it was found that the awareness of explicit knowledge of English chunksand chunking significantly played an effective role in developing the English language system in terms of fluency, accuracy, and complexity. Based on the results of this study, the researchers suggest that the explicit and declarative knowledge become implicit and procedural knowledge through prolonged and systematic practices: the explicit knowledge of L2 chunks and chunking works positively for L2 learning and use.