This paper summarized professor ZHANG Zhiyuan′s experience in using Chaihu（Radix Bupleuri）. Based on the knowledge he has learnt from the literature of doctors in past dynasties

as well as the experience he has accumulated in the clinical practice

professor ZHANG Zhiyuan makes his own understanding of Chihu in terms of medicinal nature

function and selection. Accordingly

he puts forward the "ascending and descending theory"

"heat clearing and cooling theory" and "herbal selection theory". He also gives full play to the application of classical prescriptions including Xiaochaihu Decoction（小柴胡汤） and Sini San（四逆散）

and emphasizes the modification of dosage and the combination of medicinals.