Lushan metamorphic core complex can be divided into eastern and western extensionallysymmetrical detachment tectonic belts, with welldeveloped extensiondetachment and ductile rheology structures. The western detachment belt contains one complete sequence of faulting rocks, with a solid rheological structure zone at top. The vertical stratification of an extensional structural deformation, bounded by the main detachment belt, suggests that the main detachment belt underwent the strongest deformation. Within the eastern detachment belt are developed mylonite zone and tectonic schist (gneiss) zone, and no other structures have been found on the surface. The extensional structure within the eastern detachment belt was developed on the early sinistral shear structures which were superimposed and modified. The formation temperatures of the eastern detachment belt were estimated 500~580℃ and 580~700℃ based on microscopic deformation characteristics of minerals, and the metamorphic temperature calculated by Ti inbiotite geothermometer was 613~698℃. This reveals that the metamorphism of the eastern detachment belt reached the high amphibolite facies during the formation stage. The metamorphic temperature and pressure of plagioclasitehornblende schist within the western detachment belt were 666 ~ 691℃, 0.65～0.75 GPa respectively, calculated by amphiboleplagioclase geothermometer and Al inhornblende barometer. It shows that the western detachment belt formed under the high PT conditions and large burial depth. The condition of high amphibolite facies is consistent with the eastern detachment belt. Zircon UPb dating yielded an extension age of 138.9 Ma for the eastern detachment belt, which is earlier than that of magmatic activity, but consistent with the western detachment belt. It can be speculated that the western detachment belt was the original detachment belt of Lushan metamorphic core complex, while the eastern detachment belt was the secondary detachment belt formed by gravitational equilibrium with diapirism and folding.