This article discussed ZHANG Zhiyuan's experience in using Dahuang （

Radix et Rhizoma Rhei

） based on the dose-effect relationship. Dahuang has the nature of cold， deep and storage， and can drain heat and store

yin

； moreover， it's flavor and smelling are fragrant， and keeps wandering but not good at maintaining. Based on these functions， the dosage of Dahuang is divided into small （1-3 g）， medium （6-18 g） and large （30-60 g） doses. Dose-effect relationship analysis showed that small doses of Dahuang can strengthen the stomach， direct counterflow downward， unblock meridians， and perform medicinal power， and can be used to treat all kinds of spleen and stomach diseases caused by food stagnation and upward rushing of counterflow

qi

， as well as delayed menstruation， amenorrhea and

bi

（痹） syndrome induced by obstruction of stasis blood. Medium doses of Dahuang can clear heat and resolve toxins， and is used for treating all kinds of heat syndrome. Large doses have the function of breaking up blood and attacking accumulation， and can be used to treat mental diseases. The function and its application in clinical practice can be expanded when different doses of Dahuang are combined with other herbs， such as small doses of Dahuang in combination Zheshi （

Haematitum

） and Banxia （

Rhizoma Pinelliae

）， medium doses of Dahuang in combination with Shigao （

Gypsum Fibrosum

）， small and medium doses of Dahuang in combination with Zhizi （

Fructus Gardeniae

） and Yinchen （

Herba Artemisiae Scopariae

）， and all different doses of Dahuang with Taoren （

Semen Persicae

）.