The present writer studied the medical thought of 'You-Yi(尤怡)', the medical expert of the early 'Qing(淸)' Dynasty, which can be summarized as following. 1. 'You-Yi' writed many essays and treaties about 'Shang-Han-Lun(傷寒論)' and 'Jin-Gui-Yao-Lue(金?要略)', both of which are the writings of 'Zhang-Zhong-Jing(張仲景)', the medical saint of 'Han(漢)' Dynasty, and those writings include 'Shang-Han-Guan-Zhu-Ji(傷寒貫珠集)', 'Jin-Gui-Yao-Lue-Xin-Dian(金?要略心典)', 'Yi-Xue-Dou-Shu-Ji(醫學讀書記)', 'Jin-Gui-Yi(金?翼)', and 'Jing-Xiang-Lou-Yi-An(靜香樓醫案)'. 2. A theory of 'Tai-Yang(太陽)' syndrome, including 'San-Gang-Ding-Li(三綱鼎立)', was proposed by 'Fang-You-Zhi'(方有執)' and 'Yu-Chang(喩昌)' and it came to be one of the leading theory of the 'Shang-Han-Lun', 'You-Yi' rejected their opinions in which they insisted that the 'Feng(風)' hurts the 'Wei'(衛)' and the 'Han(寒)' hurts the 'Ying(營)', and he advocated his particular idea that the 'Xie-Qi'(邪氣)' can directly hit skin, flesh, 'Ying-Wei(營衛)', the Five Organs and the Six Viscera(五臟六腑), regardless of 'Zhong-Feng(中風)' or 'Shang-Han(傷寒)', and he insisted that there is need to be anxious about Whether the 'Ying-Wei' is strong or weak. 3. In 'Shang-Han-Guan-Zhu-Ji', 'You-Yi' invented the eight classifications in treating the 'Shang-Han' and he did not follow the old theories hitherto. He divided the book into six parts via the clinical experiences, and the Classification and Logics in Treatment(辨證論治), and he put several titles on 'Jin-Gui-Yao-Lue. And he newly edited the original text of 'Shang-Han-Lun' and arranged 'Zhong-Jing(仲景)'s Six Meridian(六經) categories. Each syndrome in 'Tai-Yang' 'Yang-Ming(陽明)', 'Shao-Yang(少陽)', 'Tai-Yin'(太陰)', 'Shao-Yin(少陰)' and 'Jue-Yin(厥陰)' has its own categories in treatment. 4. In explaining the Six Meridian(六經) and the Organs and Viscera(臟腑), 'You-Yi' legislated the syndrome in 'Three Yang(三陽)' into Meridian(經) and Viscera(腑) ; the syndrome in 'Three Yin(三陰)'into Meridian(經) and Organs(腑). He also concluded that 'Shang-Han-Lun' not only discussed 'Wai-Gan(外感)' but also included the Internal Hurt(內傷) and Miscellaneous Diseases(雜病). 5. In his academic research, 'You-Yi' followed 'Zhong-Jing' in classifications and prescriptions and succeeded the theory of 'Ma-Chu(마숙)' and 'Li-Zhong-Zi(李中梓)', but was not tied to any stereotyped former practices. He put emphasis on the Spleen(脾) and the Kidney(腎) as he harmonized the Middle Energizer(中焦焦) with the taste of 'Gan(甘)' and 'Wen(溫)' and enjoyed strengthening 'Yang' by benefitting the 'Qi(氣)'. 6. He discussed in detail the causes, mechanism and symptoms on 'Tan-Yin(痰飮)' and proposed the seven categorizes in treatment. 7. He sorted the causes of 'Zhong-Feng' into two kinds of the 'Feng' via 'Wai-Gan' and Internal Hurt, and recognized these two 'Feng's correlate as mutual sources of diseases. He insisted that the origin of the 'Feng' exists in the 'Liver(肝). He also established the eight categories in treating the 'Feng'. 8. 'You-Yi' belong to the classifications and Logical Treatment School. And he, considering he respected and followed 'Zhong-Jing' and 'Li-Zhong-Zi', belongs to the successor to the 'Wen-Bu(溫補)' School. 9. His writings, especially the 'Shang-Han-Guan-Zhu-Ji' and the 'Jin-Gui-Yao-Lue-Xin-Dian', are excellent commentary works on the originals, so they served as significant guide books for many junior scholars. For penetrating the 'Shang-Han-Lun' with his unique way of classification of treatment, he has been highly appreciated by later generations including scholars like 'Tang-Li-San(唐立三)' in the 'Qing' Dynasty, and so many more ones thenceforth. In conclusion, on the base of this study, it is hopefully proposed that the still more profound research on the medical thought of 'You-Yi', as one of the most distinguished scholars, an expert clinician and an earnest writer as well.