The mafic rock is exposed in Gaoqiao area of the North Daba Mountains. It consists of diabase, gabbro-diabase, diabase-porphyrite, and pyroxene diorite, and the minerals mainly include clinopyroxene, plagioclase, hornblende and Fe-Ti oxide. The clinopyroxene, belonging exclusively to augite, was studied in detail using microprobe in this paper. The clinopyroxene has the evolution trend from Mg-richness to Fe-richness with the variation of the rock from diabase-porphyrite through gabbro-diabase to pyroxene diorite. The clinopyroxene shows high Al^Ⅳ(Al^Ⅳ=0.02～0.20, Al^Ⅳ/Al^Tot=85%～100%), and has the feature implying that the pyroxene was formed in the undersaturated alkaline basaltic magma, which is coincident with characteristics of the alkali series, as shown by the alkaline discrimination diagram of clinopyroxene and geochemistry of mafic rock. The temperature and pressure of clinopyroxene are 1 132～1 164℃ and 0.71×10²～9.30×10² MPa respective- ly, suggesting obvious deep-derived characteristics. The electric charge unbalance caused by the replacement of Si by Al is mainly compensated by Fe³⁺, Ti mainly forms titanaugite, and Al^Ⅵ enters the octahedra to form Ca(Mg,Al^Ⅵ). Because of the isomorphism of Ca²⁺ and Na⁺, the clinopyroxene has high Ca and low Na₂O. The geological background and geochemical characteristics of clinopyroxene indicate that mafic rock in Gaoqiao area is the product of extension in a back-arc basin.