The course of metaphysics is called Zhouyi. Generally, colleges and universities offer Zhouyi elective courses. Because metaphysics is a philosophical thought and ideological trend that appeared in Wei and Jin Dynasties, and it is the study and interpretation of Laozi, Zhuangzi and Zhouyi. The word "Xuan" here comes from a sentence in Laozi, "Xuan is metaphysics, the gate of Wan Qi". Metaphysics is the mainstream of thought that replaced Confucian classics in Wei and Jin Dynasties, that is, "Metaphysics". It is based on "ancestors narrate Lao Zi and Zhuang Zi" and calls Laozi, Zhuangzi and Zhouyi "San Xuan".