This research on the accurate teaching of college English aims to meet the challenges and opportunities faced by college English education under the background of globalization. The paper explores the application effect of a learning diagnosis system based on big data in college English precision teaching. The system can accurately identify students' learning needs and obstacles and provide a scientific and objective teaching basis for educators. The empirical research shows that in the experimental class of university sophomores, the accurate teaching realized by the big data learning diagnosis system significantly improved students' listening, reading, writing, and oral performance. In addition, students' learning interest and initiative also improved significantly. However, this teaching method also faces challenges such as data dependence, accuracy, technical input, privacy protection, and teaching rigidity.