This study explores a student-centered teaching method in postgraduate courses. Teacher-centered classroom teaching cannot fully stimulate learning initiative and enthusiasm of students. Student-centered means that students actively learn and construct knowledge by participating in teaching activities. This study presents a student-centered online-offline hybrid teaching method, which adopts student-centered case-based teaching and online-offline case discussion in the postgraduate courses of computer science. The latest engineering cases are integrated into teaching and a case library is constructed. Taking the digital image processing course as an example, student-centered teaching allows students to choose what to learn and how to learn. Case-based teaching makes students better understand the application of theory of knowledge. It can introduce multiple perspectives, promote understanding and reflection on problems, and help students develop higher-level thinking, analysis, and synthesis skills. This study explores online-offline case discussion method in the student-centered teaching and proposes the principles of case design of postgraduate courses. Revised Bloom's taxonomy is used for teaching assessment. The actual teaching effect shows that student-centered case-based teaching and online-offline case discussion have achieved better teaching effect.