The late Paleozoic granitic rocks are widely exposed in Donggobi Province of Southern Mongolia, which is located in the core of the Central Asian orogenic belt. The accurate isotopic dating and petrogenesis studies on 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 and 332 Ma) and two Late Carboniferous granites (320 Ma and 306 Ma) have been identified in Zamyn-Uud and Ulan Badrach. To be specific, the content of SiO2 (76.31 to 77.79 wt%) is relatively consistent with that of K2O+Na2O (8.23 8.59 wt%) in the Early Carboniferous granites, while the variation range of the content of SiO2 (72.65 to 76.22 wt%) and K2O+Na2O (7.89 to 8.67 wt%) in Late Carboniferous granites is greater than that in Early Carboniferous granites. Both Early and Late Carboniferous epochs are weakly peraluminous I-type granites, of which elements such as U, Th, K, Zr, and Hf are positive anomalies, and elements such as Sr and Ti are negative anomalies. Based on the isototopic analysis of whole-rock Sr-Nd and zircon Lu-Hf, it shows that the Early Carboniferous granites has positive εNd(t) (+3.68–+4.09) and εHf(t) (+9.70–+14.90) values in comparison to young two-stage model age of Nd (TDM2 = 753–792 Ma) and the two-stage model age of Hf isotopes (TDMc = 393–721 Ma). The above evidence indicates that the Early Carboniferous granites is 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 has higher εNd(t) (+1.17–+5.31) and εHf(t) (+13.68–+15.21), Nd model age (TDM2 = 636–984 Ma) and the two-stage model age of Hf isotopes (TDMc = 344–442 Ma), demonstrating that the material source is mainly composed of juvenile crustal materials and a small number of ancient crustal materials. Based on the existing results, the author believes that the tectonic background of the carboniferous granite records 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.