Liu is a fire theorist with the core of "reducing heart fire and benefiting kidney water". He made full use of the argument that "people injured by cold are all fever" in Neijing. In Su Wenxuan's "Original Disease Syndrome", he repeatedly pointed out: "If yang is depressed, it will be hot" and "If heat is depressed, it will evaporate sweat". At that time, doctors used the rule of law to treat colds, which aggravated the condition, so they changed the pungent-warming agent into pungent-cooling agent In the late treatment of epidemic febrile diseases, it is necessary to tonify kidney water and purge heart fire. It can be seen that the disease is not caused by heat, but by cold.

He mentioned the relationship between fire and water, heart and kidney on the basis of the saying that "the five poles are extremely hot". Water is static and fire moves, static is flat, and moving is chaotic. "Mo Ze, which moistens everything, is in Mizunokami", so if there is water on the fire, it is "auspicious", indicating that the heart is clear and the limbs are strong; If you can't make a fire under the fire, it will be "useless", which is manifested as upset face and hot feet; In terms of heart and kidney, heart belongs to fire and kidney belongs to water, and all kinds of troubles and injuries are caused by yang fire. One water can't make five fires, so heart fire is easy to flourish and kidney water is easy to decline. Therefore, the treatment should be nourishing kidney and water to treat heart fire, which is the so-called "clearing the heart and calming the nerves", which is what Dr. Wang said, "the Lord of strong water makes yang."

His unique viewpoint of "reducing heart fire and benefiting kidney water" has opened up a new way for the treatment of febrile diseases, so later doctors called Su Wan the founder of the school of febrile diseases, and it is not unreasonable for Wang Lun to say that "rivers are used for heat" in Miscellaneous Books of Ming Medicine. Zhu Zhenheng indirectly inherited the complete vegetarian theory, and under the inspiration of "reducing heart fire and benefiting kidney water", he put forward the theory that "Yang is often surplus and Yin is often insufficient" according to local conditions, which is known as "Ziyin School".