In order to determine the formation age, petrogenesis, and formation environment of the volcanic rocks of the Biyingaolao Group in Xinchengzi Basin, southern Great Hinggan Mountains (Greater Xing’an Range), Inner Mongolia, this study conducted zircon U- Pb dating, elemental geochemistry, and Sr—Nd isotope studies on the rhyolitic volcanic rocks within the basin. The LA- ICP- MS zircon U- Pb ages of the rhyolitic volcanic rocks are 132.8±0.8 Ma and 133.1±1.8 Ma respectively, indicating that the rocks were formed in the Early Cretaceous. The rocks are rich in Si and alkali, rich in potassium, depleted in Mg, Ca and P, and belong to the peralkali and high potassium calc- alkaline series rocks. The LREE and HREE were obviously fractionated, and the LREE were enriched (LREE/HREE=8.24~11.35), with significant Eu anomaly (δEu = 0.49~0.85). The trace elements are rich in Rb, Ba, K and deficient in Sr, rich in HFSE Th, U, Zr, Hf and deficient in Nb, Ta and Ti. The rocks have high Yb content and Ga/Al ratio, showing similar characteristics to A- type granites. The (87Sr/86Sr) i values of the volcanic rocks range from 0.70243 to 0.70634, εNd(t) ranges from -3.6 to -4.2, and the corresponding two- stage Nd model ages range from 1221 to 1265 Ma. Based on the regional geological data and the results of this paper, it is concluded that the volcanic magma of the Baiyingaolao Formation in Xinchengzi Basin originates may originate from anatexis of Paleoproterozoic plagioclase—amphibole rocks in the lower crust, facilitated by mantle- derived magma underplating and associated metasomatism, which is formed in the extensional tectonic setting, and may be related to the subduction of the paleo- Pacific plate to the East Asian continent. The rhyolite volcanic rocks of Baiyingaolao Formation in the basin have high U content, and the U released by the hydrothermal alteration provides uranium source for uranium mineralization in the area.