Yin deficiency is mostly due to the late stage of fever, or miscellaneous diseases for a long time, depletion of yin fluid; emotional excess, fire evil injury to the yin; room is not regular, depletion of yin essence; over-served warm and dry products, dark depletion of yin fluid; old age and physical decline, yin fluid deficiency caused by. Yin deficiency refers to the deficiency of yin fluid in the human body, its nourishment, moistening and other functions, or yin does not control yang, yang qi is overactive, to dry mouth and throat, five heart and heat (two hands and two feet heart fever, and consciously heart and chest fever), hot flashes (a burst of heat), night sweats (after going to sleep sweating abnormally, waking up sweating stops) as the main manifestations of the deficiency of the fever syndrome. Yin deficiency syndrome can be seen in the lesions of multiple organs and tissues, and the common ones include lung yin deficiency syndrome, heart yin deficiency syndrome, stomach yin deficiency syndrome, spleen yin deficiency syndrome, liver yin deficiency syndrome, kidney yin deficiency syndrome, etc., and show the syndrome characteristics of the respective organs. Patients with yin deficiency syndrome can take yin tonic medicines such as sasanqua, lily of the valley, maitake, yuzhu, dendrobium, huangjing, tortoise shell and other medicines for identification of yin deficiency. If there is a need for medication, it is recommended that it be used under the guidance of a professional physician, and not blindly self-medication.