Abstract: The course of complex functions has strong theoretical basis, rigorous argumentation system, and abstract knowledge, which makes it difficult for students to understand. Teachers should implement the PBL teaching method in course teaching. Before class, students’ cognitive conflicts are triggered and their interest in learning is stimulated by setting questions. In class, students are encouraged to think and strengthen their understanding through layered progression. After class, students’ innovative abilities are cultivated by expanding tasks to achieve good results.