Baiganhu area is situated between East Kunlun-Qimantag tectonic zone and Altun block, where the Bashierxi granite series is the key to understanding the tectonic setting of this area during the Early-Middle Silurian. In this paper, a monzonitic granite (BGH-1) and a syenogranite (BGH-4) samples were collected from a single pluton and used for petrographic observations as well as geochronological and geochemical studies. This pluton contains muscovite and garnet, and its A/CNK and A/NK ratios are in the ranges of 1.07～1.12 and 1.41～1.59, respectively. Thus this pluton is peraluminous and high-K calc-alkaline S-type granite. In addition, this pluton is characterized by enrichment of LREE and LILEs and d epletion of HFSEs, with obvious negative anomalies of Nb, P and Ti. LA-ICP-MS zircon U-Pb dating reveals that the monzonitic granite and syenogranite were emplaced at 428.2±4.2 Ma and 422.5±2.3 Ma, respectively. The data obtained by the authors and previously published data show that the calc-alkaline S-type granites and A-type granites are coexisting in Bashierxi granite series and they were formed in a post-collisional environment during the Early-Middle Silurian (433～421 Ma). However, the Early-Middle Paleozoic magmatism in eastern Qimantag between Golmud and Baiganhu fault to the east of the Baiganhu fault has recorded a complete process of Late Ordovician to Early Silurian subduction, Middle Silurian to Early Devonian collision, and late Early Devonian post-collision. Apparently, the Early-Middle Silurian magmatic plutons in eastern Qimantag and the Bashierxi granite series, which are outcropped in Baiganhu area to the west of the Baiganhu fault, were formed in different tectonic environments, thus probably belonging to different tectonic evolution systems.