Outcrops of Mesozoic volcanic rocks are quite widespread in Western Hills of Beijing.Among them, basic-intermediate volcanic rocks have phenocrysts and microcrysts of clinopyroxens. Based on a study of mineral chemistry of clinopyroxene, the author has found that clinopyroxenes are mostly augites and subordinately diopsides. The unit cell volumes, densities 183 and refractive indices of clinopyroxenes are calculated. The results show that augites have smaller unit cell volumes than diopsides. Equilibrium temperatures and pressures between clinopyroxene and melt, oxygen fugacity of magma and depth of magma chambers are computed. The depth of magma chambers of different volcanic rocks are as follows: basaltic magma of the first member of Nandaling Formation is 32km, magma of basaltic andesite and that of shoshonite-latite of the third member of Tiaojishan Formation are 24 km and 12~17 km respectively. The equilibrium temperatures between clinopyroxene and melt are as follows: basltic magma is 1229℃, magma of basaltic andesite is 1186℃, magma of shoshonite_latite is 1165~1181℃, and magma of latite is 1048~1128℃. From Early Jurassic to Early Creta- ceous, magmatic activity shows the following common characteristics: chemical composition of magma varies from basic to acid, the depth of magma chambers tends to become shallow, the equilibrium temperatures between clinopyroxene and melt change from high to low. The viewpoints are advances on the basis of analyzing mineral chemistry, rock chemistry and trace elements. The volcanic rocks studied in this paper belong to the high_potash calc-alkaline series and shoshonite series, the magmatism is controlled chiefly by partial melting, the tectonic envi- ronment of magmatic activity is mainly the inside of continental plate and subordinately island arc.