The aim of the present study was to investigate the development of theory of the deficiency of yin-yang in the spleen-stomach(脾胃). The spleen-stomach theory is a very valuable composition of the oriental medicine. Its first theoretical basis was established by Li Dong Yuan(李東垣) who wrote Piweilun("脾胃論"). He insisted the importance of spleen yang(脾陽) which is the "postnatal base of life" by transforming and transporting of food essence and fluids and raises the clear. After him, his theory had influenced many descendant medical men. one of them, Ye Tian Shi(葉天士) found out the differences of between stomach and spleen. Especially he focused on the stomach yin(胃陰) which is easy to be exhausted by dry-fire(燥火). And he also made another remedy, "the stomach yang should be moved well(宣通胃陽)", which emphasize on that cold and stagnant cause the deficiency of the stomach yang. After that, spleen yin(脾陰) theory was set up by Tang Zong Hai(唐宗海). His spleen yin(脾陰) was deeply related with digestive enzymes and pancreas, because his theory was established by comparing oriental and western medicine. These four theories became the theoretical basis of the deficiency of yin-yang in the spleen-stomach(脾胃), and similar symptom of the spleen-stomach(脾胃) could be categorized according to the pattern identification(辨證) which was developed from these four theory.