The Qilian fold belt is one of the major orogenic belts in China. Traditionally, it is divided into north Qilian fold belt, central Qilian uplift, south Qilian fold belt and Lajishan area. The study area is located at 150 km northeast of Lanzhou City, and its major part belongs to the Maxianshan Group and the adjacent Sinian and Ordovician strata(including Siergou, Tiechenggou, Tianzhusanxia Forest Park, Naxingou and Gangkouzibei).According to the mineral assemblages, microtectonics and mineral chemistry， the PreSinian metamorphic rocks, i.e., the Maxianshan Group, have experienced a complex history of three stages of metamorphism. StageⅠ(amphibolite facies) is the peak metamorphism, whose mineral assemblage is biotite+ calcium amphibole, with the conditions being 618℃ and 0.65 GPa. Stage Ⅱis epidote amphibolite facies with the mineral assemblage epidote+ albite+ calcium amphibole. Stage Ⅲ is greenschist facies with the mineral assemblage actinolite± corundophilite+ calcite. The compositions of calcium amphiboles are homogeneous. The core and rim temperatures of garnets are 418℃ and 545℃, respectively. The Sinian metamorphic rocks are greenschist facies with the mineral assemblage chlorite+ albite+ hematite+ calcite+ quartz. The Ordovician metamorphic rocks are marbles, which contain apatite layers and phlogopite.40Ar-39Ar dating of hornblende and biotite separated from amphibolite and granite yields plateau ages of 340±0.5Ma and 323.4±0.65Ma, respectively, which may represent the reactive ages of the Maxianshan Group.