The Silurian-Devonian evolution of the East Kunlun Orogen (EKO) is controversial. A-type granites are often used to constrain the timing of tectonic transformation during the orogenic process. The Baidungou granite pluton, located in the Wulonggou goldfield in the eastern part of the EKO, has not been systematically studied in previous research. Therefore, this paper takes it as the research object to study its petrogeochemistry, zircon U-Pb geochronology and Hf isotopes. The zircon U-Pb dating shows the crystallization age of the intrusion is 417.9±3.5 Ma. Petrogeochemical studies reveal that the intrusion is characterized by high silicon (SiO₂ =71.2%~77.2%) and alkali (K₂O+Na₂O=8.23%~10.7%), low MgO (0.04%~0.22%) and CaO (0.09%~0.95%), enriched large ion lithophile elements (Rb, K, Th, U), depleted high field strength elements (P, Ti), obvious negative europium anomaly, and 'gull type’ REE patterns. Combined with high Ga/Al and TFeO/MgO values and Zr saturation temperatures of whole rocks, the intrusion is classified as A-type granite. In addition, the zircon εHf(t) values vary from -0.6 to 1.9 and two-stage Hf model ages range from 1 442 to 1 284 Ma, suggesting that this A-type granite was mainly derived from the partial melting of early felsic magmatic rocks with similar Hf isotopes. This granite exhibits characteristics of the A2-type, indicating that it formed in a post-orogenic extensional environment. The EKO developed a large number of A2-type granites nearly contemporaneous with this granite, reflecting it had entered the post-collision extension stage during the Late Silurian.