Yi-Jian (simplicity) is a teaching method developed by mind educator LU Jiuyuan in the Song Dynasty. This meaningful and unique style of teaching method was a pioneer in mind education during the time of Song and Ming Dynasty.Based on the analysis of the collections of LU Jiuyuan's Works, this article aims to clarify the rationales of Yi-Jian and reveal its connotations through the interpretation of such propositions as developing one's original mind, reading for moral cultivation and the Six Classics annotating me. Then it points out the historical implications of the teaching method of Yi-Jian. The author argues that the idea that the heart is the reason is the ontological basis of Yi-Jian. Developing one's original mind refers to moral education, while reading for moral cultivation and the Six Classics annotating me refers to is knowledge. Yi-Jian was closely related to these propositions. Yi-Jian focused on stimulating and cultivating non-intellectual factors such as motivation, emotion, will and so on, especially the use of sudden enlightenment in teaching. It emphasized the cultivation of moral cognition and judgment through intuitive thinking, so it has great positive effect on moral development. Unlike the school of ZHU Xi's Neo-Confucianism education, Yi-Jian is one of the outstanding aspects of LU Jiuyuan's Mind Theory.Based on the detailed discussion of the connotation of Yi-Jian, this paper concludes that many Confucian scholars in the Ming Dynasty such as WU Yubi, CHEN Xianzhang, WANG Yangming and ZHAN Ruoshui inherited and developed LU Jiuyuan's teaching method of Yi-Jian to varying degrees.