“The mean thought” is a positive and mature thought of Confucius’s thoughts. It is a moderate thought which means “going too far is as bad as not going far enough”. The essence of “the mean thought” is “just right” and “appropriate”. “The mean thought” is the behavior standard of improving effective teaching. It can be applied in various aspect of teaching, such as building harmonious teacher-student relationship, controlling the amount and difficult degree of knowledge and correctly understanding the relation between learning time and learning effect. “The mean thought” is helpful to resolve contradictions in teaching and improve effective teaching to achieve scientific teaching, which will contribute to better development of each student with different capability.