The late Paleozoic granitic rocks are widely exposed in Dornogovi Province of Southern Mongolia, which is located in the core of the Central Asian orogenic belt. Accurate isotopic dating and petrogenetic studies of the granitic rocks are of great scientific significance for the in-depth understanding of the crustal evolution characteristics of the Central Asian orogenic belt. In this study, two Early Carboniferous granites (337 Ma and 332 Ma) and two Late Carboniferous granites (320 Ma and 306 Ma) were identified in Zamyn-Uud and Ulan Badrach. To be specific, the content of SiO₂ (76.31% to 77.79%) is relatively consistent with that of K₂O+Na₂O (8.23% to 8.59%) in the Early Carboniferous granites, while the variation range of the content of SiO₂ (72.65% to 76.22%) and K₂O+Na₂O (7.89% to 8.67%) in Late Carboniferous granites is higher than that in Early Carboniferous granites. Both Early and Late Carboniferous epochs are characterized by weakly peraluminous I-type granites, of which elements such as U, Th, K, Zr and Hf exhibit positive anomalies, and elements such as Sr and Ti exhibit negative anomalies. Based on an isotopic analysis of whole-rock Sr-Nd and zircon Lu-Hf, the authors detected that the Early Carboniferous granites have positive εNd(t) (+3.68~ +4.09) and εHf(t) (+9.70~ +14.90) values in comparison with young two-stage model age of Nd (t_DM2=792~753 Ma) and the two-stage model age of Hf isotopes (t_DM^c =721~393 Ma). The above evidence indicates that the Early Carboniferous granites were partially melted from juvenile basaltic oceanic crust, under the influence of mantle-crust interaction, showing the crust accretion of the Early Carboniferous. Unlike the Early Carboniferous, the granites in Late Carboniferous have higher εNd(t) (+1.17~+5.31) and εHf(t) (+13.68~ +15.21), Nd model age (t_DM2=984~636 Ma) and the two-stage model age of Hf isotopes (t_DM^c =442~344 Ma), demonstrating that the material source was mainly composed of juvenile crustal materials and a small quantity of ancient crustal materials. Based on the existing results, the authors believe that the tectonic background of the Carboniferous granites recorded the transformation of the regional extensional environment caused by slab roll-back of oceanic plates during the late Carboniferous to the post-collision extensional environment in the later period.