This research focuses on two themes of Sasang Medicine, ‘qi-fluid mechanism’ and ‘tae-eumin disease pattern’. These two themes are closely interrelated. Yi Jema’s Tae-eumin disease pattern holds an important position within his theory, as he himself emphasized the originality of the Tae-eumin disease pattern description. The qi-fluid concept was first introduced to the medical community by Yi, which became an important physiological, pathological mechanism within Sasang medicine. Tae-eumin disease pattern is closely related to qi-fluid concept. Yi explained qi-fluid to be managed by activity of liver and lung. The organ post(臟局) of tae-eumin is explained in terms of large liver, small lung, and deviation of the activities of lung and liver induce pathological change easily. Through liver and lung, the two categories deeply interrelate. This has been reported by numerous researchers, and the qi-fluid concept is understood to be important in the research of tae-eumin. However, research on the basic concepts ‘qi-fluid’ and its physiological, pathological mechanism has been scarce, preventing a more wider discussion on qi-fluid. Moreover, further research on the tae-eumin disease pattern discussion is also on a halt, as it needs to be understood upon the qi-fluid concept. Therefore, the objective of this research is to explain the qi-fluid concept and qi-fluid mechanism concept through studying all discussions related to qi-fluid as mentioned in Yi’s texts. The texts are 《Dongyisusebowon Sasang Chobongwon(東醫壽世保元四象草本卷)》, 《Dongmuyougo(東武遺稿)》, 《Dongyisusebowon(東醫壽世保元)》. Main concepts related to the qi-fluid mechanism are the exhalation of lung, inhalation of liver, and the triple energizer as space where qi-fluid is communicated. These concepts were objects of study in the texts. Yi suggested the qi-fluid mechanism and water-food mechanism in opposition to each other. These two constitute two axis in the physiology and pathology of the body within Sasang medicine. In order to understand the qi-fluid mechanism, the opposing water-food mechanism must also be examined. Therefore, concepts related to the water-food mechanism-acceptance of spleen, discharge of kidney, intestine/stomach, yin yang ascend/descend, etc.-were also studied in the texts. The water-food mechanism manages the bodily alignment by securing basic elements that constitute the body. The spleen and kidney creates water-food qi through the discharge/acceptance activity of the spleen and kidney, while placing water-food qi to different places, fulfilling the qualitative elements to sustain alignment. The qi-fluid mechanism acts to help express appropriate states of different people. The liver and lung respond to outside needs through the inhale and exhale activity of qi-fluid, while also collecting it to express the inner will. As the qi-fluid mechanism is an action to express one’s state as one desires, it is fundamentally related to the activity of the mind.The qi-fluid mechanism can be applied to the tae-eumin disease pattern. In Sasang medical theory, disease pattern is divided into exterior pattern and interior pattern. As tae-eumin is small lung, its exterior pattern can be thought to be caused by the shortcomings of the exhalation activity of the qi-fluid mechanism. Large liver implies that the interior pattern is caused by excess of inhalation of the qi-fluid mechanism. Based on the analysis of the tae-eumin disease pattern through aforementioned hypothesis, I believe that the qi-fluid mechanism concept could be effective in understanding the tae-eumin disease pattern. This research holds few limitations as its objective is set on building a theoretical basis of the qi-fluid theory based on textual evidence. Firstly, due to few mentions of qi-fluid concept related contents in the texts, there is insufficient evidence in defining the qi-fluid mechanism concept. Therefore, metaphor and analogy has been applied in its construction, which might have led to a less than perfect logicality in its explanation. Secondly, as literary research methods were applied, evidence to explain clinical disease patterns as experienced in reality could fall short. Despite these logical shortcomings, qi-fluid mechanism research is crucial for Sasang medical researchers, as there is an imperative to expand understanding of the tae-eumin disease pattern. Logicality will have to be complemented by further theoretical research on qi-fluid mechanism. Also, tae-eumin disease pattern and pharmacology must be reasonably explained by including clinical experience.