Pyroxene from granulite and related rocks in Qianan County has been studied in this paper, and the results show that iron content of pyroxene is obviously governed by chemical composition of host rocks: the higher the /Mg0 and =(Fe203 × 0.8999 + Fe0) values of host rocks, the higher the iron content of pyroxene. The Fe2+ -Mg distribution coefficient (KD) of clinopyroxene-orthopyroxene pair is not only controlled by tempe- rature-pressure conditions of crystallization but also affected by other compo- nents of pyroxene. Nevertheless, the Ca-Mg-Fe triangular diagram indicates that the coexisting clinopyroxene and orthopyroxene are products of equi- Librium crystallization with their average KD value in accord with the law advanced by Zhang Ruyuan et al. that the average KD value of metamorphic pyroxene is 1.85. The calculation with the clinopyroxene-orthopyroxene thermometer and an analysis of data on mineral association show that the temperature and pres- sure for the formation of pyroxene are 869±60ºC and 5 108-9 × 108 Pa respectively. TFe content of pyroxenite that shows gradual contact with the iron ore body is approximately equal to that of economic iron ore.,Tron ore is gene- tically closely related to pyroxenite.