An automatic essay scoring (AES) system used to be developed to assess students’ writing abilities in a test. However, it is recently used in the classrooms to improve students’ writing skills. Piagaiwang, an automatic essay scoring (AES) system, is widely used in China’s English writing classrooms. In this study, 56 participants are chosen from three English classes to write an essay by using Pigaiwang in order to find out how Piagaiwang enhances students EFL writing performance and how the teacher applies the big data gathered from Pigaiwang to their teaching of English writing. The study demonstrates that the pigaiwang can promote and improve students’ writing ability by providing resourceful and useful feedback and the teachers can use the big data gathered from the Pigaiwang in their English writing classrooms.