Geological characters, physical and chemical properties of clinopyroxenes from Cihai iron ore deposits are studied with X-ray diffra,ction,IR-spectroscopy, mSssbauer spectrum and mineral chemistry. Since the clinopyroxenes are cri- terion minerals in the deposits of Cihai type,the data of pyroxenes provide form an important basis for our study of the petrogenesis and mineralization. In this paper a triangular diagram with three end-members for normenc- lature of monoclinic pyroxenes is related. Theoretic.a mineral formulas of tri- angular diagram are as follows; (1) Formula of diopside-hedenbergite series, Ca(Mg, Fe)Si206-DiS; (2)Formula of minerals of clinoenstatite: (Mg, Fe)2Si206- CES; (3)Formula of theoretical minerals of tschermak; M2M1 (T206)-Ts, com- ponents of aegirine(NaFe3+Si206-Ae)and jadeite(NaAISi2O6-Ja).The three corners of the triangle represent the three components. In consideration of complicated composition of clinopyroxenes, which have the same type of crystal structure, this method is reasonable and practicable.