Abstract Li T'oegye (1501-1570), born in the period of Chinese Ming Dynasty, was a great Neo-Confucianism master in Korean Lee Dynasty. He, not only inherited from the Neo-Confucianism of Chu Hsi, but also had a full knowledge of Lu-Wang's study of human mind. Being concerned about the need of his country, he created the distinguished and unique T'oegye School of Neo-Confucianism which thus laid profound foundation on Lee Dynasty's practical philosophy. Following the motive which Chu Hsi had proclaimed in the appeal he submitted to the emperor, T'oegye wrote The Diagrams of the Learning of the Sages to serve as a teaching for the emperors. In the Diagrams, he particularly pointed out the foundamental priciple to rule a nation is to correct the emperor's culpabibility and direct the proper way for the emperors. The Ten Diagrams, the essences of T'oegye's study throughout his lifetime, are the major masterpiece of The T'oegye School. This work was thus esteemed as the "Canon" and T'oegye won the honorable title as "The Sage of Hai-Tung." (海東聖人) Chu Hsi edited Tzu Yang Kang Mu (紫陽綱目), in which he organized the major issues as the general outlines and the minor issues as precise items. In the present paper I will follow Chu Hsi's way of editing; first, I will illustrate the general outline of thoughts in T'oegye's The Diagrams of the Learning of the Sages to present its magnitude and profundity; second, I will analyze the precise items of thoughts in T'oegye's The Diagrams of the Learning of the Sages to distinguish its exactitude and exquisiteness. By this way, the system of thoughts of The Diagrams of the Learning of the Sages will be brilliantly illuminated.