Liu Wansu (劉完素 Líu Wánsù; 1110–1200) was a Jin dynasty Chinese physician. He observed the high frequency of fever and inflammation in serious diseases and promoted the idea of using herbs of cooling nature to treat these conditions. This was a step in the opposite direction of many of his predecessors, who focused on using warming herbs. This work had much influence on the later concept of "wen bing" or epidemic febrile diseases, which corresponded to (and preceded) the Western concept of contagious disease. He also undertook a detailed study of the Nei Ching Su Wen Jing Su Wen, describing the etiology of disease in relation to the teachings of that famous text.

He is credited with founding the Cold and Cooling School and developed the theory of similar transformation. The body』s host qi is yang, therefore warm. Hence any evil guest qi, either externally invading or internally engendered, will tend to transform into a warm or hot evil similar to the body』s host or ruling qi. He is considered one of the four great masters of the Jin and Yuan dynasties.

劉完素（12世紀約1100年 - 1180年），字守真，自號通元處士，河間（今河北河間市）人，世稱劉河間。金元四大醫學家之一，研究五運六氣，為「寒涼派」的創始人。

發揮《內經》理論，提倡火熱論，並重視針灸治法，臨床施治重視井穴、原穴。並喜用五腧穴，以火熱論思想指導針灸臨床，形成了以清熱瀉火為基點的針灸學術思想，對金元以後的醫家影響很大。因創製不少治療傷寒熱病的方劑，故後世稱他為「寒涼派」。

劉完素的著作有：《黃帝素問宣明論方》、《素問玄機原病式》、《宣明內方》、《內經運氣要旨論》、《傷寒直格》、《傷寒標本心法類萃》、《三消論》、《素問藥注》、《醫方精要》。