"Kong Yan Zhi Le" is an important issue in the Neo-Confucianism of the Song and Ming Dynasties and the whole Confucianism.At the same time,it has been being full of controversies for a long time.On the light of the realms of You and Wu,all kinds of theories on the issue is analyzed and summarized.The two characteristics in common are found among the theories that the realms of You and Wu are united,and the thinking pattern is the Golden Mean.The differences are the connectors and the way of the realms of You and Wu.The united realm of You and Wu manifests the Neo-Confucianism in the Song and Ming Dynasties surpassing the ancient classics,the inosculation with the Buddhism and the Daoism,and the consequence of "Kong Yan Zhi Le" during the foundation,the development and the evolvement of the Neo-Confucianism in the Song and Ming Dynasties.