Effective teacher intervention is the key to the success of College English Reform in China. Guided by the Humanistic Constructivism and based on “the Mediation Theory”, this paper reports and analyzes an experiment with “process-based teacher intervention” in oral English class. The experiment indicates the superiority of the innovative teacher intervention model over the traditional one in terms of teaching goals, teaching materials, strategies and oral project management. Meanwhile, the “process-based teacher intervention” plays a facilitative role in promoting learners’ motivation, teamwork, oral English fluency and accuracy.