This paper explores how to teach English writing to big classes in China from the task-based perspective. Based on a comparison between the traditional 3Ps approach and the tasked-based approach, the paper proposes a practical linear procedure as to how to teach English writing in the task-based classroom to big classes. An empirical study is conducted in the form of questionnaires to test the effectiveness of this task-based procedure to foreign language writing in the Chinese EFL setting. Results show that the task-based approach is effective to teach big classes English writing, as it deepens students' understanding of the task-based approach and enhances various aspects of writing. However, there are several factors calling for future attention, such as teachers' roles, monitoring and evaluation in the practice of task-based instruction. It is hoped that this proposed procedure of task-based approach can serve as an inspiration for other foreign language teachers and stimulate more studies in task-based learning and teaching.