Constructivism theory reveals the regularity of human cognition. According to constructivism theory, students will learn best by trying to make sense of something on their own with the teacher as a guide to help them along the way. Discrete mathematics is a very important course for computer majors. As discrete mathematics has quite rich contents and it is very abstract, it is not easy for students to master its spirit. In this paper, we propose applying constructivism theory to the teaching of discrete mathematics. During all the teaching phases (including teachers' preparation before class, teaching during class and students' review after class), constructivism theory is used. Our practices show that constructivism theory based teaching method can raise students' learning interests, and also can help them to understand the course better.