“Left liver and right lung” is an important theoretical issue in traditional Chinese medicine(TCM).There have been many explanations since it was put forward，and these explanations are different.Based on the theory of manifestation，root cause，and medial Qi in the five movements and six Qi，this paper analyzed the theory of “left liver and right lung” and thought that the theory indicated that “the liver governs Yang，and the lung governs Yin”.Its theoretical connotation has good guiding significance for clinical practice.